I do have a few Macs that are stuck on pre-Ventura OSes and for which I don’t necessarily need iCloud connectivity (except for Music, which does, in fact, work fine when you disconnect from iCloud.) So I’m getting myself ready for this going forward to see if I can run those Macs disconnected from iCloud but still have them be useful so I can turn on ADP.
Two of them are Mac Mini that I use basically as iTunes/Music media servers, one of which stores the canonical version of all of our ripped CDs, plus, of course, purchased iTunes tracks and now some tracks from Apple Music. One of them also runs SpamSieve as a spam filtering drone for all of the email accounts we have that don’t have strong server-based spam filtering. (Wonderful product and solution.) For these, I don’t need access to contacts, calendars, iCloud Drive, Notes, Reminders, etc. - I just need the ability to connect to the iTunes Store and to my Apple Music account, plus the email accounts in the Mail app. And, yes, I can do that (this I’ve already been doing on one of the Mac Minis.) I’ve also been using one of the Mac Minis to connect to the iCloud Photos and be the source of backup offsite and to Time Machine, but that I can no longer do after disconnecting from iCloud - for that I have transferred that function to an iMac that can run Ventura and I will use that computer for this.
My bigger issue is my old 2015 MacBook Air which I have kept as a backup to my 2022 MBA, and that I also use during the summer when I am my main home while we have moved up to the summer house with the 2022 MBA. (Yes, I know, first world problems.) The 2015 is stuck at Monterey.
I’m not all that worried about losing access to Messages and FaceTime on the old MBA - I don’t like using Messages on the Mac anyway, and almost all of my FT is from my iPad or iPhone. Reminders - I use this a little, but I’m ok with having them only my phone and iPad. I really don’t need them on my Mac. Notes - this one is tougher. Notes I use mostly as a list of things that I want to read later, but it’s also a convenient way to transfer info between computers. For right now, I am trying out the app Agenda as a Notes replacement for that, and the Notes app itself I’ll use just for ephemeral content (such as scanning documents using the iPhone camera) and for private info that I lock with passcode / FaceID / TouchID.
Also, the iMac I mentioned before is at home, so I can really just use that. The main issue is going to be if the 2022 MBA fails and I need to use the 2015 as a backup until I get it repaired/replaced. (For that actually I think I would just disable ADP temporarily and reconnect to iCloud.)
So to get ready for this, I’ve moved almost all iCloud Drive content to my Sync dot com syncing service (a service similar to Dropbox, but a bit less expensive and with a nicer MacOS app).
As for this:
As I have said, Mail is fine. Calendars I have solved by sharing my calendars to another iCloud account that I will not be turning ADP on and then adding the other iCloud account to Calendars; I can now get calendars on the 2015 MBA.
Contacts: that’s tougher. There seems to be no way to share contacts with another account as you can calendars, Apple doesn’t have shared family account contacts, and I can’t find a way to access an iCloud account from within Contacts unless you are officially connected to it. And my Apple ID is not an iCloud account, so I can just connect to iCloud as a secondary account and sync contacts (unless I have missed something.) But, the truth is, I don’t think that I need this. If I ever need an email address from anywhere, I can just share the actual address in an Agenda note (or email it to myself) and manually add the contact to the 2015 MBA. (I had thought about using my fastmail account as my main contacts repository, but connecting fastmail contacts to iOS seems to be a bit of a pain, requiring either a profile, which I’d rather not do, or a non-SSL carddav server. I could use my old gmail account for contacts, but I’d rather not. I’ll just manually export them and maintain them manually, as listed above.)
Agenda: the first wrench in this plan was that Agenda syncs using iCloud by default to sync. However, it does support syncing via Dropbox, so I’m trying that out. I had to do some manual editing to some notes that wouldn’t sync (just changing their name forced a sync, then I renamed them back).
One last thing that I’ll need to do is go up to the summer house and upgrade the Apple TV there to tvOS 16.2. After that I should be able to try out ADP.
Unless you are 100% on 16.2 and 13.1, this isn’t easy.