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.
Depending on the launcher and launch method you may need to set systemd variables. Look at the way
50-systemd-user.conf
works https://wiki.archlinux.org/title/Sway#ConfigurationI use the following fragment to make sure the cursor theme propagates to applications launched with wofi: https://github.com/StaticRocket/dotfiles/blob/main/dot_config/sway/systemd-user.conf