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Didn't really consider postmarketOS. I haven't played with installing mobile operating systems on desktop hardware in a long time.
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Yeah I think what screwed my testing was applications that were using xwayland without me noticing. The stable firefox snap at the time (which is preinstalled on Ubuntu), uses it apparently. I have only used Xorg before, as I've never felt the need or desire to step into the tarpit that's migrating to Wayland.
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Neat workaround for your tablet, glad it works well for you.
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End of the day, I'm sure that I could have puttered on it and eventually got it all working (aside from the hardware on the surface that appears to be completely locked down), but it's a pretty poor showing out of the box. YMMV and all that, and I hope that more investment in the space makes it a better experience in the future.