I had installed some gtk4 apps with flatpak just out of curiosity to make sure it's not my customization that is causing gtk4 apps to render the fonts unreadable and in some cases there's no text at all. There are missing images, thumbnails for the videos.
Some gtk4 apps installed with flatpak are looking exactly how they should, but there's still some which are having the same problem as they were installed natively.
But at least I can use some of them in this way. š