Deleting a partition

[pbesong]

I bought a used Macbook Pro (mid 2012) that had 3 partitions on it, Big Sur, Catalina, and another that had a generic name. I forget what it was. Anyway, I could not boot into the Catalina partition. It would always hang halfway through, so I reinstalled the original OS (mountain lion), then upgraded to Mojave. I'd like to get rid of the other 2 partitions now, but Disk Utility won't allow me to delete them. I deleted the Big Sur partition, but it's still showing a total of 3 disks. the other 2 besides Mojave disk are grayed out. I can't boot into them either as they're not an option under Startup Disk, only Mojave. I simply want to wipe the computer completely and install Mojave. How do I do that? Here is a photo of what Disk Utility is showing. I have Mojave installed on Disk 2 (Macintosh HD). The other 2 disks are using 60gb of disk space each. I want to reclaim that for Mojave.

Also after rebooting I always get a message that says "This disk uses features that are not supported on this version of macOS". How do I get rid of that too?

 

[KeesMacPro]

IMO The easiest way is to make a createinstallmedia USB with Mojave installer .
Boot from the installer , open Disk Utility and delete Apple SSD SM512E... ,(delete the main device, not a container or partition).
Choose GUID partition and APFS and install Mojave to the internal disk.
Note that you should have a backup of your present Mojave install before deleting the Apple SSD.
After this clean install , use Migration Assistant to recover all your data from the backup .

 

[pbesong]

That worked perfectly. Thanks! I used something called Disk Drill to make a bootable disk after I downloaded Mojave. It made it pretty easy. No terminal to deal with. It got rid of that pesky incompatible disk message too after I installed Mojave. was hoping it would. Thanks again!

 

[KeesMacPro]

Good to hear that!

That message was probably because of the Big Sur install , APFS format is developed since Mojave (1st gen) to Big Sur (3rd gen).
Another pitfall with APFS is to install another OS inside a container of an existing OS instead of on a completely separate partition.

 

[pbesong]

that makes sense. i got the laptop with the sole purpose of being able to run apps that Catalina and Big Sur no longer support. just can't do without them!

 

[KeesMacPro]

Mojave is known as a very stable OS , and the last OS that supports 32 bit apps

 

[pbesong]

Yep! That’s why i wanted it. Too bad they can’t run legacy apps in a pseudo emulator.