Click on the Partition tab. You will be prompted to either add an APFS volume or a Partition. Click Partition. Click the Add partition button it looks like a plus (+) symbol. Change the size of the partition you wish to use by dragging the resize controls. The used space is represented in blue. Of course, you still need to have the needed free storage space on your Mac as a whole to contain the new macOS version. For Macs with APFS file system, Apple recommends creating a new volume within your current partition when attempting to install a separate macOS version in addition to your current one. I want to install Mojave on a separate APFS volume on my mac running Catalina so my wife can switch between OS to be able to run some 32 bit games she loves, but I can't even run the 'install' as it says: 'This copy of the “Install macOS” application is too old to be opened on this version of macOS'.
Why Do I Have Two Apfs Volumes
In past years I've had a spare Mac I could use but that Mac can't run Monterey so I'd like to install Monterey on a separate APFS volume on my M1 MacBook Pro. I've read the instructions here:
Installing Macos On A Separate Apfs Volume Download
https://support.apple.com/en-us/HT208891
but I want to be certain I don't causes issues with the Big Sur installation. Obviously after backing up, I use DiskUtility to create a new APFS Volume.
If I download the macOSBetaDeveloperUtility.dmg and install it, then I think it will give me the option to update the OS (as that's what I did in the past, but it's not what I want to do this year). From screenshots here:
https://support.apple.com/en-us/HT208891
I think it will allow me to choose where to install and I can choose the new APFS volume I made for the beta. Is that correct?
And then after the installation, will the Big Sur volume work as before or will software update in it want to update to the Monterey beta instead of letting me do any Big Sur updates that come out this summer?
And then at some point after the official Monterey release, I assume I can just delete the APFS volume I created for Monterey to test my apps and then update the Big Sur volume to the official version of Monterey?
Are there any mistakes in my steps/plans?
Thanks,Dave