If you're running #phoc's development branch (main, tracking #wlroots git) on a device with split display controller and gpu (like the #librem5 with #etnaviv and mxsfb / dcss) make sure to set
WLR_RENDER_DRM_DEVICE=/dev/dri/renderD128
export WLR_RENDER_DRM_DEVICE
in ~/.phoshdebug as otherwise GTK4 (and lots of other things) will fail to render anything. GTK3 and #phosh itself will work fine.
This doesn't apply when you run nested of e.g. with intel graphics.
If you're not developing for phosh or phoc you can ignore this and the above entirely.
Background is that check_import_dmabuf in wlr_linux_dmabuf_v1.c picks the wrong node for it's validation (https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3757) so we have to help it a little bit for the time being.