Two Macintosh HD drives showing up on my desktop.

[AdamNC]

I just got the computer today. It is a 2020 13 inch Intel i7 the 10th gen version. It was on Big Sur when I got it. I put 15.7.3 on it using Mr Macintosh. Before that I erased the drive so it was clean. I just got done setting everything up how I like my settings. Shut it down and restart and that bottom one popped up after 5-10 mins. It appears to be a duplicate of my drive. In disk utility it shows it and it says there are 6 volumes shared. What did I screw up and do I have to start all over and how do I fix this. Both “drives” show all the apps and such. Thanks.

 

[DeltaMac]

This is part of the APFS setup, and yours looks pretty normal. The "-Data" drive is the one you have access to. The other (Macintosh HD on your system) is Read-only. Again, part of a normal APFS drive arrangement, since Big Sur.
As both drives exist, there's nothing that you need to do.

 

[Nermal]

No, it's not normal. The two volumes should be "joined" and should only appear in Finder as a single volume. I'm not sure how to fix it though.

 

[AdamNC]

I decided to go with the nuclear option and re wiped the whole drive and all. It is a lot smoother and less lag.