Unable to upgrade from Mojave to Catalina because my disk is not formatted to APFS

If you want anything on the drive, back up before doing anything else.

Boot into internet recovery (Cmd-opt-R) and use Disk Utility to erase the drive completely.

Then, reinstall MacOS.

In Disk Utility, select Show all devices from the View button menu.

Select the Drive, then Erase button.

Choose GUID Partition map and APFS.

Quit Disk Utility and Reinstall macOS.

If you want to restore data, Migrate your data from the backup when Startup Assistant ask what you want to do.

Apple provides non-destructive methods for start-up disk drives for APFS conversion, and hence no data (files or folders) will be lost.

side note: On the other hand, APFS formatting will erase all the files and folders stored on the external hard drive. If not backed up earlier, APFS formatting on the external drive will cause data loss. Even with the start-up drive, one may delete or lose files from the APFS formatted media.

Non-Destructive APFS Conversion

Restart the Mac into Recovery Mode.

Recovery: https://support.apple.com/en-us/HT204904

Launch Disk utility.

Click-select your named boot volume—the default name is "Macintosh HD" —(Not the physical drive above it.)

In the Disk Utility> Edit menu> select “Convert to APFS"

Are you sure your mac is running Mojave, that does not look like the Disk Utility GUI for Mojave,

if it were you would have the View option in the menubar. And you would also have APFS

options in the Erase> Format selector.

Boot your mac back up normally and check under > About This Mac what OS you are actually running.

I resolved my issue by erasing my drive using MaxOS extended format in Disk Utility; then reinstalling MacOS (it installed Sierra).

i then downloaded High Sierra from Apple.com and updated my computer, which automatically converted my drive to APFS.

Finally, I was able to update to Catalina.

Sorry. I had considered suggesting this, but figured there should be an easier way.

It really isn't that bad, though. As a test, recently, I installed Mountain Lion on an External SSD, then upgraded to El Capitan, then High Sierra, Mojave, and finally Catalina. It only took about half a day to complete all of it. That certainly is affected by your internet download speed.