Lost macOS generated password, can't recover it, not sure how to recover?

I got the onboarding process started, but there were some notifications about errors that needed to be fixed, and I thought rebooting would solve them. No such luck.

After rebooting, I no longer have the strong password that macOS generated for me (I thought it would be saved), so I’m locked out. It looks like I have to reinstall HA, but I don’t know what to do here. I downloaded the file needed and Balena Etcher, but all I can do is select the file to flash… I can’t select a target to proceed.

Where do I go from here?