Yep, I have tried this too, but didn’t solve those… but going further I have started to review other config files in home directory and found this environment variable defined in .bashrc:
export QT_QPA_PLATFORMTHEME=qt6ct
removing this solved this issue! I am trying to figure out how it was added here. Maybe very long time ago and wasn’t doing anything because I didn’t have qt6ct installed before.
Thank You @rugyada for your patience and help!