Titlebar not scaling
I use a HiDPI display and therefore had to adjust settings for scaling. In the meantime, I was able to adjust everything perfectly so that all applications (including GTK) scale appropriately.
The only application that has problems at the moment is this one. The titlebar does not scale at all. After a little inspection I noticed that Manjaro Hello does not use a titlebar in the classic way. Instead, it looks like the titlebar is inside the application itself and the titlebar that would normaly actually be generated and controlled by the system is simply hidden. This means that the corresponding settings for scaling the titlebar, which work without problems in other GTK applications, do not work. It is not only unaesthetic but also tedious to use the titlebar buttons as you have to click very precisely. (Minimize, Maximize & Close)
Screenshot attached:
Above: Titlebar for all other applications
Bottom: Titlebar at Manjaro Hello
TLDR: Some settings for titlebar customization can't get passed to Manjaro Hello.
Software info:
Manjaro Version: 22.0.0
Kernel: Linux 6.0.8-1
Graphics Platform: X11
KDE Plasma Version: 5.26.3
KDE Frameworks Version: 5.99.0
QT Version: 5.15.7