Just found out no font gets rendered in any of the ToneLib apps (GFX/Metal) anymore – both standalone and VST3 plugins in Ardour.
I have found out the culprit to be the fontconfig updates from the last couple of syncs (fontconfig 2.15), i.e., downgrading back to 2.14 fixes the issue for me (also tested this with both fresh and updated Solus images in VMs to replicate the issue as well as confirming it's nonpresent in Fedora and Pop!_OS ones).
Unfortunately when on 2.15 and launching the apps via terminal nothing gets printed at all. Also had zero luck finding anything related to it in the logs...
Any help, advice on what else to try/check next or idea as to which change to the fontconfig could be culprit to the issue is greatly appreciated!