Looks like psensor uses low res icon (14x14) in sys tray. Also no context menu for psensor.
New to Manjaro, sorry for noob question.
It happens only in Manjaro KDE.
So it may be a problem of Plasma theme, because Manjaro uses own, default theming. Change it and see if it helps.
The issue of Plasma 5 theming is that there is no consistency in icons where it comes to sytray, because some are inherited by icon theme and some from Plasma theme, depends on Plasma theme… This creates an icon-chaos and inconsistencies. This will be changed in Plasma 6.
Do you have the indicator package(s)?
pacman -Qs libappindicator
If you dont have libappindicator-gtk3 already then install it.
libappindicator-gtk3 already installed.