A feature that a lot of Apple apps have that doesn't seem talked about much is they can use standard protocols and not require iCloud.

Mail.app/Reminders.app/Notes.app can use IMAP, Cal.app with CalDAV, and Contacts.app with CardDAV [1].

It doesn't offer a lot of the features iCloud has like advanced formatting or collaboration, but is a useful for simple standards based syncing and portability.

I've done this with my iPhone/Macs and Fastmail for the last few years and it works great [2].

1. https://support.apple.com/guide/iphone/set-up-mail-contacts-...

2. https://www.fastmail.help/hc/en-us/articles/1500000279941