I could also solve the problem for me (T14s, AMD R5 processor). Seemed that the amdgpu driver was not loading fast enough? Finally I added it (amdgpu) to the modules ind /etc/mkinitcpio.conf, now GDM is starting automatically.
I could also solve the problem for me (T14s, AMD R5 processor). Seemed that the amdgpu driver was not loading fast enough? Finally I added it (amdgpu) to the modules ind /etc/mkinitcpio.conf, now GDM is starting automatically.