Why twm? Have you considered using a modern but non-bloated Wayland compositor like sway, using applications that natively support Wayland where possible and Xwayland where needed? I imagine that would make much more efficient use of the GPU that the Raspberry Pi has always had.
Hm, I'm usually not a fan of using new stuff unless it has been stable/working/default for some years... last I heard of wayland was NOT good, but it was a couple of years back... The way you should use the GPU is with OpenGL, 2D can get along without hardware acceleration, I don't see how wayland can be better at using OpenGL as that is the application who calls the GPU directly without going through the window manager!?
I said 2 years ago I would switch to the Raspberry 4 as my main driver, but it's still on my side monitor, with the keyboard on the side!!!
I'm waiting for higher KWh prices... probably next winter I'll have to switch!