Plasma-5 will be unsupported and cleaned up rather sooner than later. This package hasn't had a release in years, it does not seem like there is any development going on. Does it even do anything in a Plasma-6 environment?
I think it's time to drop fcitx4 related packages. Currently all fcitx4 packages are bumped to fcitx5 (but some of them are not yet STABLE). Packages related to fcitx4 are already in maintenance. The upstream repository for the core package app-i18n/fcitx:4 has been archived, fcitx4 will not have support for the Plasma-6 environment.
*** Bug 939192 has been marked as a duplicate of this bug. ***