Hi Gang.
I have been receiving the following message on my girlfriends Mac upon startup:
Any recommendations on how to solve?
She’s running:
12" MacBook 2015
macOS Big Sur
Many thanks indeed,
Ben.
Welcome!
I would follow the instructions at the link below, including booting into the recovery system. There’s a link for how to do that on the webpage.
Hopefully it’s something that DiskUtility can repair!
Hi @JohnAtl
Thank you for your reply.
Bad news, I ran First Aid on all disks and in recovery mode too and no luck. We still have the same message appearing on booting up.
Any other ideas?
Really appreciate it 
this might be useful - do you see 2 data drives in disk util?
If you are seeing 2 - did you see this message?
NO NEED TO SHUT DOWN OR RE-INSTALL ANYTHING!!
There’s likely no need to erase and all that. I just got off the phone with apple and they guided me through to the disk utility, Macintosh HD - Data had been duplicated and the second one was greyed out. they had me click on the greyed out Macintosh HD - Data and then click the “-” to remove the disk. It was removed and I restarted and it’s perfectly fine. Hope this helps.