GTK4 apps from Flatpak/Flathub fail to start with the new GTK4 rendering backend

On certain devices (Adreno-based GPUs, e.g. OnePlus 6) Flatpaks apps using GTK4 might fail to start with a currently unknown reason.

As a temporary workaround, you can start flatpak apps with GSK_RENDERER=ngl as environment variable.

The relevant issue is on https://gitlab.postmarketos.org/postmarketOS/pmaports/-/issues/3655.