I can no longer migrate my library from PC to mac
So, I've been using iTunes as my main music library on my PC for over a decade now, and I've been periodically backing it up to an external hard drive, and then copying it to my iMac and opening it up there with all my playlists, play counts etc intact for all that time without a hitch, using iTunes on Mac and the later 'music' iteration of the app.
Doing my backup as normal and when I option-open the music app on the iMac to point it at the .itl library file music just sticks on 'loading' forever and nothing happens. Before, upon reading said file it would immediately open my library fully intact and away I went.
I've tried deleting the library and re-copying it from the hard drive, making changes to the 'master' library on the PC so it overwrites the .it file, then copying it back to the Mac, and nothing, the same thing happens. I have even tried copying it to another iMac at work which is on OS 12.5 and on that machine when I option open the library it just tries to open the music app but with no music (but doesn't stick on loading like it does on my Mac that's on 12.6) I can't seem to find anything online about the music app suddenly not being able to read this critical file, has anyone any ideas? I've never had this problem before.
iTunes on my PC is updated to the latest version and is working perfectly.
iMac