Can NOT downgrade on iMac with Preinstalled Catalina

[NoBoMac]

^^This might work.

I could be well off base here as I've never done this, but seem to recall can't use a newer version of MacOS to install an older version, even if just to an external drive. Seem to recall that would need to wipe the Mac, install the OS you want, install to external, then re-upgrade back to what the Mac was at. So wipe, Catalina on Mac, Catalina to external, Ventura back onto Mac.

 

[greyeyezz]

^^This might work.

I could be well off base here as I've never done this, but seem to recall can't use a newer version of MacOS to install an older version, even if just to an external drive. Seem to recall that would need to wipe the Mac, install the OS you want, install to external, then re-upgrade back to what the Mac was at. So wipe, Catalina on Mac, Catalina to external, Ventura back onto Mac.

Ventura is on my internal. If I wipe my internal will the option to install Catalina be there? The virtual drive is an idea if I had a larger drive.

 

[MacGeekYYC]

Another strategy - pick up a used Mac Mini 2012 or newer. Used 2012's are pretty cheap these days. You might even be able to get by with just a Mini. Set it up using your keyboard and mouse from the iMac. If you have anything at all in the house with HDMI, you could use that as the display while installing Catalina, then run the Mini headless with access through screen sharing.

 

[NoBoMac]

Shift-Option-Command-R boot should install Catalina.

Virtual, can put the VM on an external drive. That’s where I keep my VMs (Samsung SSD).

 

[bogdanw]

All is fine but I need to run some older software and printer drivers that only work with Cat.

What printer drivers? Some can be installed in Ventura https://forums.macrumors.com/threads/how-to-install-unsigned-printer-driver-in-ventura.2378871/

 

[greyeyezz]

Another question will Catalina boot a Ventura clone?

 

[MacGeekYYC]

Another question will Catalina boot a Ventura clone?

I'm reading your question in a couple of ways.

1) booting a virtual machine and 2) seeing a Ventura volume from Catalina

For 1, if you're thinking of creating a Ventura virtual machine guest on a Catalina host, from reading the Fusion system requirements you might be able to do it with Fusion 12.1.2. This leads into another can of worms about licenses and commercial software. The VMware Fusion free player starts with version 13.

System Requirements for Fusion

Verify that you have the minimum system requirements for installing and using Fusion.

docs.vmware.com

2) With the APFS changes between Catalina and Ventura, Ventura can mount a Catalina APFS drive while Catalina won't even see a Ventura drive.

APFS versions, updates and compatibility

What’s in APFS, and what are its tools? How to interpret the version number, and what do we know has changed with different versions? How compatible are they?

eclecticlight.co