No longer able to manually add artwork to my iTunes library albums

I recently was unable to manually add artwork to my albums in iTunes. So I reinstalled the Microsoft Store version of iTunes on my Windows 11 machine, reconnected to my database and most of my artwork appeared, but not all of it. I was unable to manually add artwork to those albums missing artwork. I also removed the artwork from an album and was unable to add it back. Next, I created a new database and repopulated it with my albums and songs from my media files. I am still unable to manually add artwork. I stumbled upon being able to create artwork for the duplicate of an AAC audio file song if I create that duplicate via File > Convert > Create AAC Version. Some albums missing artwork have AAC audio files. Others have MPEG audio files. Also, when I select Add Artwork and pick an album cover from my file system, I see the Album Cover appear, but it does not get saved when I click the OK button. Apple Support's suggestion was that I upgrade to the Apple Music app which is not an option for me as I have the original artwork for 3,565 albums that I converted from vinyl albums and ripped from CDs. I do not want to do anything that risks integrating Apple's artwork with my artwork. Any suggestions regarding how to fix my problem with not being able to add artwork manually?