Separating photos by Apple IDs on a shared iMac

My wife and I have our own apple laptops and iPhones on different Apple ids, plus a family shared iMac with only one user account using my ID. This Q is about photos on the iMac. We don’t use messages, shared icals, or have any music that matters under my ID on this iMac.

Until now this shared iMac has used my Apple ID for all services. However, I haven’t ever shared photos from my phone to that iMac because I take a lot for work they don’t need to be there. Instead, we would like all of my wife’s iphone photos to go to that iMac. Obviously we don’t want to lose years of photos and videos there from many sources.

What’s the best way to do this? I would prefer not to have separate user accounts but will if needed. (It will just stay logged in as her unless I needed to do something.)

Is it as simple as switching the iMac to her Apple ID, deleting mine, and then sharing photos from her phone? If so should I create a new user acct for her on the iMac first for safety? And when we share from her phone, is that photostream or iCloud photos? Lastly, will apps I’ve bought on the iMac go away? Again, probably fine if I have to switch ids to use something.

We’ll have all backed up to a drive and to Backblaze first of course.

Thanks so much! 🙏🤞