Stuck upgrading from Yosemite to Catalina…which path to take?

Today helped someone with a 2012 MacMini running Yosemite. (long story...husband died 7 years ago with the admin password, she's just now getting around to working on it). My job is to get it to upload all of it's photos (156GB) to iCloud, so she can continue onto life with an iPad and iPhone only.

Of course Yosemite is outdated and I'm pretty sure doesn't have the security requirements to sign into iCloud Photos. So, I thought a logical step would be to update the macOS. Got Catalina installer going (the latest OS it will take).

After install, it presented its various startup windows. Got to the "upload crash logs to developers approval" screen and clicked Continue. Nothing has happened since. It's that same graphic, grayed out because presumably it accepted the press of the 'Continue' button. While we were waiting for it, I could hear the hard disk crunching away -- presumably doing the HFS+ to APFS conversion. We let it crunch away for between 30-60 minutes.

Since then, the crunching has stopped, but the graphic is still on the "crash log question" screen -- no desktop.

Should we.... 1) power cycle it and hope for a full boot up?

2) assume it's still busy even though the crunching seems to have stopped?

3) boot into Recovery Mode and run some Terminal command to make sure APFS is in place?

4) boot into Recovery Mode and reinstall Catalina?