iCloud+ Family Sharing Compatibility

I want to use iCloud+ Family Sharing with my family, but my desktop machine is an iMac (21.5-inch, Late 2013) which apparently can't be updated beyond Catalina 10.15.7 This computer still runs fine (I've upgraded the drive to SSD), so I don't need to change it!

It states I need MacOs 11 as a minimum requirement. I have a MacBook Pro running Monterey 12.6.5 and iPhone and iPad on iOS 16, which will all be fine, but does that mean I won't be able to use iCloud+ successfully on my iMac? I back up to Time Machine, so back up isn't a major issue, but does it mean that I will lose syncing of Calendar and other Apps?

Incidentally, when I log on to iCloud on the internet from my iMac, it tells me I have iCloud+ already... I'm a little confused and don't want to lose the ability to sync all my machines!

Any ideas?!