Syncing photos, events, Albums etc between iMac and iPhone

I've recently migrated to a new iMac using Time Machine and whilst realise that iPhotos no longer works in 15.3.1 I'm having a lot pop issues getting to grips with the Photos App. Before I started I imported all my iPhoto albums and database into Photo on my old iMac. All of these appear on my new iMac (Success).

Previously I would connect my iPhone to my iMac, import any pictures from the phone into iPhoto, create Albums or Events and then choose which Albums (and Events) to transfer back to myiPhone with iTunes. It worked perfectly.

Since upgrading the iPhone to 18.3.1 (horrible upgrade) the iPhot 'Events from you Mac' shows the events, but no photos in them. Some, but not all, of the Albums are there. When I went back to iTunes to try and import them again (after converting some events to Albums) there was no option to select the Albums I wanted to include?

All I see in iPhot is a list of:

Media types

Recents

Recently Saved

Shared Albums

There is no list of all the Albums in Photos on the iMac to choose from.

I didn't really want to use iCloud to sync all my photos as I have far too many, and some Albums/Events I simply want to keep on the iMac and not add to the iPhone (which would run out of space)

Surely it can't be that difficult?