Cannot downgrade Catalina, even with Internet Recovery, even with USB sticks

[cyberstudio]

Bought a 2013 iMac to experiment with Catalina. Didn't have any Time Machine backups because it was a "new" machine to me. To do some development work I wish to have High Sierra, Mojave and Catalina on the same machine. I didn't think about this too much because I thought Internet Recovery would bail me out if I did something wrong, so I went straight from Mavericks to Catalina which, hindsight 20/20, was the totally wrong order to do things.

I have USB sticks with High Sierra and Mavericks, and also since the machine was 2013 Internet Recovery is supposed to put it back to Mavericks. But Internet Recovery offered to install Catalina with no option to install anything else! There is some hidden Catalina recovery partition... I am primarily a Windows developer and I don't know that much about Macs, but it's some macos base system? Catalina took over that and the machine stubbornly refused to install anything lower.

When I tried the High Sierra stick it says my Catalina drive is locked, so I just used Disk Utility to wipe it clean and put it back to Mac OS Extended (journaled) but High Sierra still says it cannot install on that drive. The same is true for Mavericks.

What shall I do?

 

[dsemf]

Bought a 2013 iMac to experiment with Catalina. Didn't have any Time Machine backups because it was a "new" machine to me. To do some development work I wish to have High Sierra, Mojave and Catalina on the same machine. I didn't think about this too much because I thought Internet Recovery would bail me out if I did something wrong, so I went straight from Mavericks to Catalina which, hindsight 20/20, was the totally wrong order to do things.

I have USB sticks with High Sierra and Mavericks, and also since the machine was 2013 Internet Recovery is supposed to put it back to Mavericks. But Internet Recovery offered to install Catalina with no option to install anything else! There is some hidden Catalina recovery partition... I am primarily a Windows developer and I don't know that much about Macs, but it's some macos base system? Catalina took over that and the machine stubbornly refused to install anything lower.

When I tried the High Sierra stick it says my Catalina drive is locked, so I just used Disk Utility to wipe it clean and put it back to Mac OS Extended (journaled) but High Sierra still says it cannot install on that drive. The same is true for Mavericks.

What shall I do?

In Disk Utility, did you set view to All devices? You need to erase at the top level, the entire disk.

DS

 

[gilby101]

To do some development work I wish to have High Sierra, Mojave and Catalina on the same machine

Install Catalina for everyday use and load other macOS versions into virtual machines under VMware Fusion (or Parallels).

 

[cyberstudio]

Thank you for your responses! I burned a couple of more days on experimentation and I think I realized what my mistake was. I had a fusion drive and that was to blame.

Apparently only one operating system could be master of how the SSD and the spinning drive were integrated, once I install a new operating system on an APFS Volume, it gained control of the entire fusion drive and prevent any previous operating systems from booting or even from them reinstalling or uninstalling! Indeed, if I try to erase the previous operating system with Disk Utility it just hangs.

I was new to this fusion drive thing, and came to the realization that it was impossible to install 2 operating systems on it (unless only one of them used fusion but all the rest were partitioned to use the spinning disk only). I wished the installer had warned me of this, but thankfully, fusion drives were becoming a thing of the past as SSDs increased in capacity.