I just purchased a 2018 Honda Accord and am experiencing something similar. However, I can't find a way to change artist or album on my vehicles main screen, at all. There is a "browse" button, but it is always grayed out, even if I am in park. The only way I can change artist or album is through my phone or by using Siri. I can only change the volume or move between tracks using my vehicle's controls.
Your ‘18 Accord might be different from my ‘17 Civic, but here’s my guess anyway —
The music you’ll see in CarPlay reflects what you can see in the Music app. That’s the first thing.
Me, I don’t want to use cellular data to download my iTunes-based music while on the road, so I scroll down to Downloaded Music and tap it. Then I can use only the music that I’ve loaded onto the phone, thereby treating it like an iPod.
My guess about your issue is, you’re seeing tracks that you own but aren’t on your phone, and you also have the settings for downloading music turned Off.
Does that make sense? I can take some screenshots later. (another cool thing about CarPlay is, when the phone is connected and CarPlay is active, doing a screenshot on the phone also creates a screenshot of the car’s display)