I wrote this earlier in the thread...
Hi All
I have reverted back to 12.6 and recovered apps etc. Here is a simple way that I did it.
Step 1. Go to applications folder in finder and find itunes app
Step 2. Right click on itunes icon and select GET INFO
Step 3. Expand the sharing & permissions section so you can see the padlock. Click on the padlock and unlock (you need your password). Click on the privileges for everyone and change it to read and write. Close the get info window.
Step 4. Go back to finder and drag itunes to trash.
Step 5. Download itunes 12.6 here Download iTunes 12.6.2 for macOSand then turn off your wifi.
Step 6. Install itunes 12.6
Step 7. You will then see an error message saying "The file 'itunes library.itl' cannot be read becasue it was created with a newer version of itunes.
Step 8. Go to your itunes folder in finder. Look for username\music\itunes and locate the .itl file.
Step 9. Check the date and time of the file and then drag it somewhere like the desktop.
Step 10. Still in finder, look for the folder 'previous itunes libraries'
Step 11. locate the itl file in here which is just before the update and drag it into the itunes folder where you previously removed the newer file.
Step 12. Open itunes.... voila!
Step 13. Go to preferences in itunes and uncheck 'check for new software updates automatically'.
Step 14. Turn wifi back on...
Step 15. breathe eeeaaassyyyyyyyy...... lol
You also need to turn updates off in App store settings....
Cheers