2015 MacBook Air stuck in reboot loop during Mojave > Catalina upgrade – any way to view logs/errors?

I’m trying to update my 2015 11" MBA from Mojave (latest patches) to Catalina (newest version of installer). I have >20GB free disk space and I’m running the installer from a USB stick created using the official utility in the Catalina installer package. I have also reset the PRAM/NVRAM recently and run a disk check.

The installer gets to the black-screen, Apple-logo stage and after a while says "Estimating time remaining" but the progress bar never advances beyond about 30% (near the "n" in "Estimating). After a few hours (not sure of an exact time) the machine will reboot and the same progress bar will appear and start to fill again. But it never advances beyond that position or completes.

Most recently, I’ve left the installation for 8 days to no avail. Before that I was able to abandon the installation and use Recovery Mode to restore Mojave, exactly as I’d left it, and retry the installation from there.

Is there anything I should try in this situation, and perhaps more importantly, is it possible to view logs from the installation process to try to figure out where it’s getting stuck? I’ve seen Cmd+L mentioned in a few places but hitting this at the black-screen stage does nothing.

If needs be I can just restore Mojave again and continue using that, but my other machine is running Catalina and I’d like them to be running matching versions if possible.

Thanks in advance!