Catalina upgrade stalled. How to proceed?

Press and hold down the Power button until the computer shuts down. Wait 30 seconds then restart the machine. If you boot into your Mojave system, then do the following:

Repair the Drive for El Capitan or Later

1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Utility Menu appears.
2. Select Disk Utility and press the Continue button.
3. Then select the indented (usually, Macintosh HD) volume entry from the side list. 
4. Click on the First Aid tab in the toolbar and wait for the Done button to activate. Click on it, then quit Disk Utility.
5. Select Restart from the Apple menu.

Retry the Catalina installation. If you did not save a copy of the installer in your Downloads folder, then you will have to re-download Catalina: Download macOS Catalina from the Mac App Store.

When I try this I just get same black screen with progress bar at about 15% and it doesn’t move.

Continuing from above. Estimating time remaining at 9 minutes for a few hours now. No progress.

Continuing on #3. Running first aid. Now it seems stuck on “checking snapshot 1 of 22”.