The term fragmentation is IMHO the best word to describe wayland. And that’s the reason why this page exists. While traditional “three lines” (XMODIFIERS, GTK_IM_MODULE, QT_IM_MODULE) also mostly work under wayland, but there is some other way to setup and special care needed to make all application works.

Hopefully I covered most of things in this wiki page: https://fcitx-im.org/wiki/Using_Fcitx_5_on_Wayland

Also, you are always welcome to contribute to fcitx’s wiki. https://fcitx-im.org/wiki/Contribute_to_this_Wiki