Create a hybrid tank spec.

4 of my 8 chars each have a hybrid tank spec for tanking content up to vet dlc (they could, but it's a selfish setup so they use more supportive measures instead).

Each of them runs Nirn on the backbar (from their stamina dps sets, so it's a greatsword with berserker, not crusher on) while frontbar is Order's Wrath, Stormfist and Masters sword and shield (for around 5k resistance and heal).

By doing this I'm about resistance cap, usually with 35k health, 28k stamina, 18k magicka (sugar cookies as food) and pull 25k dps on bosses, which is half what it'd be as a full dps, but sufficient (most also run lovers as mundus stone)

The key to understanding ESO is that your dps is from your gear, not your skills. Because every class can be every role at any time, they have to put the damage in passives for the armor, as well as in the sets themselves. So to create a tank that can also dps, you give up something. Thankfully, a tank can build for 50k health but by giving it up.
To meet resistance cap I rely on major resolve (on some), minor resolve (from vigor) and masters sword and shield, which adds about 14k resistances - this is good enough to enable me to bring some dps in a tank build.

I'll give you some options that I use. I play Brawler builds. My single-target damage in dungeons is typically something like 15K, while AOE damage is "through the roof". Soloing time for vMA is about 1 hour in a pure solo variation of the stamsorc. vBRP arena 1 can be soloed with the stamsorc up to the boss. Soloing of everything up to vet hard mode City of Ash 2 is possible with a pure Brawler build (mechanics permitting). Also takes just over an hour.

For vet DLC dungeons I switch to one of the builds that includes 1H+Shield. In case of the stamsorc I do this with a gear and skill change only (Dressing Room addon on PC). In case of the DK, it's a completely integrated build for maximum flexibility. The DK is stronger as a pure tank that can perma-block, but it neither has the healing nor the Brawler sustain of the stamsorc. This makes the DK stronger in groups and for higher-end content, such as vet DLC (HM) dungeons, but the stamsorc in Brawler guise is stronger for solo play and solo carrying or finishing of fights where the rest of the group has died. E.g. the builds have different limits. I play all normal trials plus Craglorn vet trials with these builds too, using the 1H+Shield variations.

https://en.uesp.net/wiki/Special:EsoBuildData?id=478307
https://en.uesp.net/wiki/Special:EsoBuildData?id=489325
https://en.uesp.net/wiki/Special:EsoBuildData?id=487819

As ever, the devil's in the details. Let's talk about the Tormentor set first. I adore this set. It turns Stampede into an AOE taunt, due to the ground AOE of that skill, and it turns Silver Leash and Unrelenting Grip into a taunt. In the case of Grip, you either manage to pull and taunt the target at the same time or, if pulling is not possible, you taunt ranged targets for free. The time advantages (taunt + pull in one skill), the cost advantages of Grip, the AOE taunt, those are all real benefits for your playstyle and they save slotting a separate ranged taunt. The only downside of relying on Tormentor for taunting is that it does not taunt bosses that are in an invulnerable phase.

In addition Tormentor grants you extra resistances, which means that, together with the new Resolving Vigor, you easily reach the resistance cap in medium armor. Why is this good? Because medium armor has the block cost reduction (not heavy) and it doesn't kill you to dodge roll once in a while. You also deal more damage, which we also want to do in a hybrid tank / DD / solo build.

Heavy armor normally contributes to block sustain via the Constitution passive. We do not need this anymore. DK can sustain via Cinder Storm spam / Earthen Heart passive. Note how the efficient tri-stat cost reduction enchants nuke the cost of that skill into the ground while also turning Pierce Armor spam into a very cheap heal from Master's 1H+Shield. This is the main self-heal of the DK build. I don't even run Coagulating Blood, because I feel it's too expensive. Pierce Armor costs stamina, but only 800 stamina is this build. You can freely taunt and heal with that.

The stamsorc, meanwhile, sustains from Dark Deal and Vicious Ophidian in the Brawler variant of the build. This also gives us Minor Slayer and 43% crit overall. Master's 2H + Caltrops deals serious damage to mobs. Single target damage is not very good, but pulling adds with Silver Leash can help regardless of whether you are the designated tank or playing solo.

The stamsorc has some carefully orchestrated health and healing. Gold Food, Bound Armaments and Strategic Reserve CP ups your health regen to 3.5K. We basically never use the ultimate. Bound Armaments passively and permanently also ups your health. You could use the Clannfear in it's place, but I find the Clannfear very situational. It's an expensive heal and it tends to run off and aggro targets that then get isolated and you end up having to kill separately after the main fight. The Clannfear is a waste of time more often than not. Therefore we rely on health regen, the Brawler shield, Crit Surge (another reason to build for decent crit), Dark Deal and Vigor. This adds up to a lot of ongoing self-healing and shielding, something you will really feel as opposed to every other build I know. It beats magplars by a country mile in terms of survival. Investing into Brawler sustain also beats shielding sets, such as Hexos Ward, Prayer Shawl, Iceheart, and so on, because Brawler spam refreshes the shield every second and the shield can get very big (about 20K) when you hit multiple targets. No set nor combination of sets can match that shield size with that uptime. Maybe it can, if you make a point of combining all the available other shields, but I think it's far wiser to invest into sustain and damage and get the Brawler shield as byproduct, if you want to be this tanky and still accomplish something.

The only way you could get still better healing is by adding Pale Order as a solo player. In that case I ditch Tormentor for either Order's Wrath on both bars and a Maelstrom 2h back bar (no Pale Order), or I backbar Wretched Vitality (with Pale Order). To get the absolute most out of the Brawler shield, you need sustain, sustain, sustain. This is how you can solo parts of vBRP and not get bogged down into defense by Dark Dealing while fleeing from the mobs half the time. Do not underestimate how good the Brawler shield becomes when you have the sustain to spam that skill. Medium armor and Vicious Ophidian, I feel, are also indispensible to make it work at it's best.

As to that ultimate, I used to use Temporal Guard for the Minor Protection, but that is so weak these days, I find it more useful to slot Precognition. That skill can break you out of half the unbreakable stuns in dungeons that would otherwise kill you as a solo player or if the group has no experience and doesn't break you free in places like Fang Lair (Ulfnor) or Cradle Of Shadows (second last boss).

The 1H+Shield variation of the stamsorc explores some alternatives. It's a pure tank wearing Yolna, in part to make higher end and trial groups happy who care about tanks providing that standard buff. It can't perma-block like the DK, but strategic use of Dark Deal and Introspection, the latter of which yields 30% damage reduction, manages our stamina.

The DK build tries to do the impossible and combine a blocking and Brawler spec into a single build. This a bit of an oxymoron, since Brawler thrives on stam sustain and blocking cuts it off (I must experiment with that new magicka blocking mythic). The end result is a build that is even more a jack of all trades, master of none. It can't maintain Brawler and has lower damage, but it can switch between Brawler and perma-blocking playstyles in a single fight. Different tradeoffs. The good thing about the DK is the extremely low block cost and ability to hunker down with Cinder Storm spam. It helps when you don't know the content well.

The armory system solves this for me. I main a DK tank and my typical dungeon setup uses magma incarnate, turning tide and drake's rush. Using armory I switch to a solo build with different attributes and CP stars where I use 2h greatsword, bow, 5-pc tzogvin, 5-pc briarheart, ROTPO, and one item piece with stam recovery. Works beautifully.