Font problem: Boxes instead of characters in some applications

Hello, I'm dealing with a very annoying problem: Since a recent fresh install of Archlinux, I have a problem with fonts in some applications. Some areas that should show legends/labels of functions, show boxes with letters and/or numbers in them. This happened in Audacity and Cecilia so far (see attachments) and I'd rather see the problem fixed than avoiding the applications that have them. I'm using Archlinux with realtime kernel (RT-Linux 5.4) and some applications necessary for my requirements, including said affected applications. I have installed a few fonts recently that I use for my desktop along with pscircle as part of my desktop background. Did I mess something up? If yes, what could it be?
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