@arubislander, you nailed it, thanks.

I switched to "20.04 Development" and everything seems to be working.

(They look like Desktop apps running on a phone, but I don't know why I expected anything different. And I've heard there are workarounds.)

Cheers

I've installed UT Fossa on a Pixel 3a XL, and then installed a couple of apps via Libertine (e.g. Firefox and Kodi).

None of them will start. They all:

• show a window with a logo and a spinning circle
• then open another window, called "X11 support", which is completely black. (The keyboard also appears.)

Any ideas? Are there any logs I can check?