Re: Cannot get hotspot working on desktop

I finally solved this, I think.

The full details are now in the bug report
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1106398

TL;DR: The hotspot was set up reasonably, so that packets going
through it are forwarded for handling by the rest of the system. But I
had previously used Docker on this system, and *it* set up a forwarding
rule which allows forwarding from/to the docker network, but not any
other network. And that rule was having the last word.