Welcome to my world. I've been subjected to this for years now. The game disconnects me so often that I can no longer do any group activities (trials, dungeons, PVP, etc.).
Same thing has been happening to me for the last 4+ hours, I've never had this issue before.
I've tried all of the suggested and commonly known troubleshooting steps to no avail. The only thing that worked and still works is using a VPN, unsure as to why exactly this helps but it does, no more issues. This isn't a real solution, but it's a temporary fix as I don't intend to be paying more than I'm paying already to play ESO or use a free VPN that will have terrible connection, as well as log and sell my data. I don't have this issue in any other multiplayer title or even website or VPS for that matter, just ESO.
Might be some technical issue between ESO's megaserver (EU) and my ISP. All thought my ISP doesn't use CGN and solely uses NAT so I'm not sure what could be the issue.
EDIT: Changed my DNS settings in Windows from my ISP's (default) to CloudFlare's (1.1.1.1 and 1.0.0.1) and now the game works, no disconnects. Odd.