I have partially transitioned from macOS to Linux, in my experience the main thing is to migrate services such as email and passwords. Once you’re using something open source for those on your I devices you’re way less locked in. iCloud wise I’d recommend getting a managed nextcloud instance. It has a lot of the features you need and provides platform agnostic sync. Also, you don’t need to manage your own it security which is a plus is you’re not super technical.

I have been dumpster diving after components recently, it’s crazy what people just toss out.

Holy shit I was googling about this yesterday and was only finding useless reddit threads