I have tried every solution listed that I could find and none of it works. The server loads fine, but the client side game crashes upon opening the quest book.

May I please ask for detailed instructions on how to move the quests from singleplayer to a server in 1.16.4?

The crash had to do with task logic meant to be done server-side being performed client-side, which should be fixed with #564.

crash-2021-02-01_01.54.46-client.txt

You will want to share the crash log