Gems and endeavours are only used to purchase items which are in crown crates.
Gems are a compensation system - you get them from useless duplicates and junk consumables and use them to buy things you actually wanted. Endeavours are complying with Microsoft's loot box policy that anything in loot boxes will be earnable by playing.
I don't think they've ever had an item in the crown store and in crates at the same time. Sometimes crown store items are later added into crates, but that could be months or years later and I'm not sure it happens to all of them.
PC EU player | She/her/hers | PAWS (Positively Against Wrip-off Stuff) - Say No to Crown Crates!
"Remember in this game we call life that no one said it's fair"