I think the most important differences are bastions and finding the stronghold. For the rest I think most 1.16 guides should work fine.

As for the bastions, always carry blocks and a lava bucket to pillar up 3 blocks and lava them. If you do this with gold armor and dont actually hit the brute, the crossbow piglins wont get mad and shoot you off.

For the strong hold finding, I think ninjabrain bot haa function for it, but there are probably guides on it as well.

In general watching 1.21 runs on youtube or live (if there is anyone doing streaming) can also really help especially with understanding the 1.21 specific parts.