The mobile build of Godot 4.0 isn't finished. I tried to test it, but there were glitches. In theory Vulkan has some pretty big gains on mobile. However, you need a newer device to even support it. Older devices won't work at all until OpenGL support is finished. I can't really make any guess as to whether it will be fixed as there are too many unknowns. I think at this point, developing 3D on mobile will require a decent phone.