Syncing music to iPhone from Windows shows inconsistent artwork

I am adding my older music files (RIP'd from my ancient CDs of yesterday before mobile phones). They are on my Win 11 laptop in M4a and I have made sure the cover artwork is embedded in JPG at 850 x 850 pixels. Add the album on Apple Music on the Win 11 laptop and then with iPhone connected use Apple Devices to Synchronising them across. Sometimes they don't even go across? But quite often they go over but Apple Music on iPhone 12 doesn't display the cover Artwork (that is embedded). Sometimes on the Win 11 machine I get a second art work labelled folder. I wish I understood this nightmare. I have done this in the past on my Samsung Android phone and haven't had all these problems. Seems to me Apple wants me to pay for Apple Music Subscription then it all will work. I used to purchase music via iTunes (before Apple changed it over to Apple Music). These files are in the my Apple Library and stream or download fine. Shame about all this problem with my older music library Apple. Any ideas Forum. Thanks.

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