Unknown error while trying to install Catalina

Having this issue two. Attempting to upgrade from Mojave to Catalina. Tried hotspot, tried reimage, LAN direct connection. Nothing works if it's network related.

Luckily I had an old external hard drive and created a bootable installer.

https://support.apple.com/en-us/HT201372

Took much longer, but was able to upgrade. Had to turn off SIP and allow bootable devices setting enabled to upgrade.

You might try this:

Reinstall El Capitan or Later Without Erasing Drive

Please be sure you back up, if possible.

1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
2. Select Disk Utility and click on the Continue button.
3. Select the indented (usually, Macintosh HD) volume entry from the side list.
4. Click on the First Aid button in Disk Utility's toolbar. Wait until the Done button activates, then click on it.
5. Quit Disk Utility and return to the Utility Menu.
6. Select Install OS X and click on the Continue button.

I'm seeing this at work now too. We're unable to update from Mojave. No option to downgrade our customer's Macs. The 2018 Mac minis are too new.

-Doug