iTunes Library.itl cannot be read after macOS rollback from 10.14 to 10.13

I recently rolled my macOS back to High Sierra from Mojave as my older iMac was better suited to High Sierra. Now I'm getting the error 'The file "iTunes Library.itl" cannot be read because it was created by a newer version of iTunes. Update your macOS to install the latest version of iTunes.'

I'm only able to run iTunes 12.8.2.3 which is not compatible with my ex-Mojave iTunes Library.

My version of High Sierra is macOS Extended HFS+, not APFS, which I think is part of my problem.

Any tips on how to convert my ex-Mojave iTunes Library.itl to run under iTunes 12.8 would be greatly appreciated!