How to Transfer Music from iPhone to iMac?

I have a bit over 20 gig of music on my iPhone and USED to have the same on iTunes on my intel chipped imac.

I tried Apple Music as a test and since the prompt said I could and should upload the rest of MY tracks to iCloud, I did.

Then I decided that Apple Music was not worth the cost and canceled Apple Music.

Poof. 90% of the tracks (my personal property uploaded to Apple Music in iCloud)are gone from my iMac.

iMac is running 10.15.7

Can I erase the music library on the iMac and copy the music from my iPhone to the iMac?

How?

[Re-Titled by Moderator]