Where is my music?

I have an old iPhone SE (the first one) and I've never had any issue with the thousand or so songs in my iTunes library. Then I bought a 14" MacBook Pro. Now half my music is inaccessible on both my MacBook and my iPhone 11. When I try to listen to many songs I already own with my MacBook, it says I need an active subscription to Apple Music while some other songs actually will play. The same music that isn't available on my MacBook also isn't available on my iPhone 11, but all my music is accessible on my old SE. Am I actually expected to pay for a subscription to Apple Music in order to listen to material I already own?? Where is my music?

I forgot to mention - when I open iTunes on my MacBook, it says it's updating my cloud library. It said that for a day and a half before I gave up.