Part of the problem is Phosh is basically fucking GNOME and inherits all the GNOME enshittification including a render path that requires considerable CPU/GPU oomph to draw smoothly. Windows has a smoother UX on old/weak hardware than GNOME. I don't know why this is and why they can't (or won't bother to) get their act together, but when it comes to a responsive UI, a bare X WM that uses regular 2D draw calls trounces GNOME. On the PinePhone that pretty much means SXMO.