Hi,
I've installed the SO Beta on OpenSUSE Leap 15.4 via RPM package with YAST. I immediately noticed that the filetype icons from the SO package are not in use anymore. That's how it looks for me now:
As you can see, the original SoftMaker types (prdx, prsx, pmdx, tmdx) have no icon at all and are marked as unknown. The third-party types (docx, odt etc) are shown with the system icons instead of the icons from the SoftMaker package (/usr/share/officenx/icons/). I tried to set up the icons for these types manually in the system settings, even copied the PNG icons to the system icons folder and converted one of the icons into SVG for the test purpose - nothing of this helped. I use ePapirus icon set, but the issue is the same when I switch to the other icon sets, including the default Breeze theme.
My configuration:
KDE Plasma 5.24.4
KDE Framework 5.90.0
Qt version 5.15.2
By the way, Windows version of Beta doesn't have this problem, the proper icons are shown "out of the box" right after the installation.