If it doesn’t even boot from the USB stick then it’s probably a hardware issue.

They are trying to make money to stay afloat. Postmarketos is a community project so it’s not comparable. And neither Purism nor Pine64 seem to be huge commercial successes just like Jolla, though they seem to be doing a bit better.

They have been owned by a Russian state-owned telecom corporation for a few years until recent events (Russia currently tries to push Sailfish OS fork as its “russian-made” mobile OS). Original Finnish management has split off to a new independent company with the same name last year, and this looks like their last ditch attempt to continue existing. I don’t expect they will last much longer (the reason why they were bought by Russia in the first place was that Jolla failed as a business).

Qt 6 has been out for more than three years now.