Can't read or eject a CD-R that was created as a backup CD on a PC.

I'm trying to read a stack of CD-Rs that are marked as Backup Media. They were probably created on a PC running Windows. I put one in the external CDROM on my iMac, running MacOS Big Sur 11.7.9. Can't read them. Finder does not recognize them. Can't eject them.

I've been able to read CD-Rs that were created in Windows, but this set will not read and will not eject.

Trying to recover some critical data from my sister's computer, which will not run.

Does Back-up create a file format that my iMac can't read or handle?

Very frustrated. Help Please!

Thanks,

veehbj