Cannot install OS Catalina

The disk on your machine is partitioned using MBR, which is very old.

Catalina will only install on GUID partitioned disks (like Windows10, Ubuntu, or any other recent/newer OS)

Backup your data which is on kerbyINTERNAL to another disk to save your data.

Delete all partitions, repartition the disk using GUID scheme, install Catalina...

After it you can recreate the kerbyInternal partition (or Volume because GUID/APFS gives you this better possibility) and copy your data back to the disk on the new partition/volume after installing Catalina

(see picture above to compare to yours)

Any other questions feel free to aks

The erase is not available when we are trying to delete/modify the partition of the current system we have booted.

You will have to create any USB bootable install stick (or CD-ROM), and boot via it, to do.

Unfortunately there is not much options.. you need to boot the machine to anything else external , to be able to delete its partition of the internal HD

Complement:

any external USB hard disk also does the job,

or [if] you have a fast internet connection you can do the internet recovery. it also makes it possible to remove all partitions of the internal HD

kerby23 wrote:

Its MacBook Pro 13'' mid 2012. Its running Mac OS Mojave 10.14.3 (18D109)

It is the same MacBook model I am using right now to reply to you, it runs perfectly and smooth the latest Catalina

MacBook Pro (13-inch, Mid 2012), 2,5 GHz Intel Core i5

You are going to love it with Catalina, but make sure it has at least 8GB or more RAM. (8GB is sufficient, anything more is for fun)

How old is the machine? What are you running currently?