Apple Music today vs years ago

Back ground: I have large library of music (16+ GB) that was saved to iMac HD. Put together way back from downloads, copies of old CDs & digital downloads purchased through iTunes. Never wanted to 'subscribe' to new apple music, so music files left unused on iMac. Eventually I added to icloud for storage & security from deletions. Now when I look at my files I see: user/Music/AudioMusicApps-GarageBand-Music/Media/all my files. When I look on my icloud drive: Music/AudioMusicApps-GarageBand-iTunes-Music. The Music folder has a few sub folders, but they are all empty. The iTunes folder contains AlbumArtwork-AutoAdd to Music-A couple libraries files-iTunesMedia-iTunesMusic. iTunes Media has folders for downloads, home videos,podcasts & Music. All my music files in the Music folder here. The folder located in the initial iTunes folder on icloud drive called iTunesMusic has some various files&folders that look like iTunesMedia, but are generally empty.

NOW: Trying to sync more music to iPhone. Cable iPhone to iMac, go through what I used to do and nothing is there. Open MUSIC app on iMac. Look in Library, choose recently added and see my whole listing of music files, but when I choose to play, I get nothing. When I choose Artists, I see them all, but most are grayed. That doesn't matter because none of my files play.

I'm too old to be interested in the most recent music out there. All I want to do is listen to my existing library via CarPlay in truck. Suggestions for best way to organize and sync/play my music..... please