Reverting a 2017 Catalina iMac back to a 32bit Mohave?

[slope]

Bought a new 27" Fusion drive iMac in July 2018 from John Lewis installed with Mohave.Happy as Larry and pleased as Punch cos I could still run Photoshop CS5 and Office for Mac 2008.

But during a security upgrade it borked completely. Several less than successful telephone calls with different and difficult to understand very swift speaking Apple 'gurus', it was diagnosed as a probable old skool HD gone nuts.

Fortunately I still had all the packaging and therews still 6 months JL extra 2 year warranty remaining.. It was duly packed and shipped back to the store I originally purchased it from mail order (don't have a car and don't DO trains). This is of course a risky business as no courier in the world will insure an iMac for damage in transit, only loss. (JL and all the other suppliers must take a punt wit fingers crossed?)

Fortunately it arrived back after 3 weeks repaired but with Catalina installed. Like a dumn a**e I backed up my previous Time Machine Mohave and High Sierra stuff. So the last Mohave on it is from September 2109.

It appears I can't just reinstall everything up to date now, as if I want go totlly back to Mohave - all the Catalina stuff will have to be manually transferred?

Is this correct and how would I go about such a thing? Any one know of an idiot's guide to help?

Bascically I miss pre subscription Photoshop and prefer Excel and Word (don't use Presentation or whatever its called). I do have Affinity Photo but am struggling with my pea brain and its way round things - mybe `i just need to buy the book or go on a course - only need it for photo editing and none of that fancy modern stuff.

[Gattopardo]

Thought that you could reinstall everything from time machine.

Basically it is a reinstall mojave.  Log on to the apps store and mojave should be there in your purchase history.

Do you have installation stuff (discs) for the software you want to

[Jaded]

Also look up reinstalling OSX from the Recovery partition. I believe there is an option to put the version of OSX that was originally on the machine back on. Having said that, if it is an older one, you may not then be able to upset it to a version prior to Catalina.

[Jurek]

I remember reading somewhere (may've been here) that it isn't possible to install a regressive MacOS.
ETA - I think I've said it before, the ability to run pre-cambrian software is the reason I have two iMacs.

[grams]

It’s very hard-to-impossible to downgrade *iOS*, because all installations are verified against Apple’s servers and they normally only authorise the most recent one or two.

MacOS has no such limitations. Just find the old installer, make a new partition and install. The installers are readily available online. As Jaded says, installing from the recovery partition sometimes gets you a surprise OS downgrade.

(Edit to add: IIRC the installer doesn’t let you install an older version on top of a newer version on the same partition)

The hard part is untangling your old data and apps from the upgraded partition. There are too many variables and different approaches to go into what you might actually do.

I guess the starting point is knowing where you are now - is your stuff on the Catalina partition, or on a backup drive?

[Jaded]

https://support.apple.com/en-us/HT204904