I use VLC,Keepass,Kdenlive and few other QT Apps on my sway setup. So, wanted to configure their themes from Sway. I installed qt5ct and qt6ct and did export QT_QPA_PLATFORMTHEME=qt5ct in bashrc and .profile. While runnin echo $QT_QPA_PLATFORMTHEME it is showing qt5ct but it is not working showing that error message that QT_QPA_PLATFORMTHEME need to be set as qt5ct or qt6ct when launching from .desktop But when launching from terminal they start and function properly but do not change any theming.
In my experience setting environment variables is pretty inconsistent. The easiest way would be using /etc/environment. This sets stuff globally for all users and definitely works.
PAM also used to support a per-user environment file, but that’s deprecated or removed even. The best you can do for per-user config is setting variables both in your login shell and the systemd user environments file.