What is the reason for this policy to not update pamac-gtk to pamac-gtk3 ? My manjaro XFCE was first installed in 2017. I think pamac-gtk stems from this date?!
I got trouble with pamac highlighting in pamac history and i learned: update to pamac-gtk3 and the issue is gone.
I even wrote a senseless bug report for pamac 
I’m shure the devs have a good reason for this policy?!!
Actually it is a downgrade. gtk4 → gtk3
I think you are mistaking a few things. 
pamac-gtk is the GTK4-based version of the pamac GUI, while pamac-gtk3 is the GTK3-based version.
In other words, pamac-gtk3 is an older design than pamac-gtk. GTK4 is currently only used by GNOME and GNOME applications. If you’re on XFCE, Cinnamon, MATE, Budgie or even Plasma (which is not GTK-based), then you’re better off with pamac-gtk3.
Besides, pamac-gtk — i.e. the GTK4 version — requires the installation of separate and distinct plugins for FlatPak, Snap and the AUR, while pamac-gtk3 supports all of that without any plugins.
(Edit: The latter is no longer applicable.)
Pure GTK4 was supported since years ago on Plasma KDE. The problem is that LibAdwaita library (used by GNOME apps and built on top of GTK4) that moves with every upgrade, and GNOME devs keep playing with it and refuse to provide a standard API to theme LibAdwaita based apps on other desktops. Most provided themes are just a result of trial and errors of modifying some CSS files and will break with each LibAdwaita upgrade.
Plasma devs are not going to release some temporary working theme that is gonna fails in the future, and they are still waiting for GNOME devs to abandon their selfish ideas.
@medmedin While technically related, this thread is already solved and any further discussion into upstream practices and opinions about them is off-topic. However, feel free to create a new topic in our Member Hub if you would like to discuss the topic further.