sddm is broken in alpine (again) so I just switched back to greetd+regreet and fixed the weird large cursor issue (which involved adding support for setting the GTK cursor-theme-size option) and figured out how to hide the titlebar (passing -d to cage to disable CSD)

I should publish my regreet patches somewhere (or send them upstream, but the patch adding a suspend button definitely isn't ready for that since it doesn't make it optional)