If I have done the dragonflight campaign and got adventure mode and world quests, If I switch realm will I have to do the campaign again to unlock those again.
Nope. Not even if you faction change.
Things like adventure mode and other unlocks are account wide. Not realm wide my friend
Okay cool thank you
You could even roll a Horde on a new realm. You would have adventure mode. As long as your toon is on the same account unlocks are account wide. Same with mounts