tanxiety is a very real phenomenon because tanking necessarily requires you to take initiative
as a former tank main, the best advice i can give is to watch your (good) tank while you're on another job, see what cooldowns they use where, where they put the mobs, etc.

take screenshots of where the tank pulls mobs and look at them afterward. if you're a healer, pay attention to the defensive cooldowns they use and how that affects how much you have to heal them while it's active, and translate that to your own tanking experience.

the hardest part of being a tank is removing the fear of the unknown. arm yourself with knowledge.
also: if someone is giving you shit, just abandon the duty. sure, you get a 30m penalty, but next time you queue will almost always be near instant. they have to wait for backfill.

YOU set the pace of the dungeon. don't even say anything - just abandon if people are being assholes. you get yourself out of a miserable situation, and they'll now spend more time in the dungeon than they would have if they just kept their mouth shut and pressed their buttons