If you prepare for a case like this then it's easy. If you get caught off guard (like I imagine most people will) it's hard.
I have an unhealthy habit of switching between FOSS and Apple a few times a year (don't ask) and generally it is pretty easy. The most annoying thing to me is Photos export, especially if you don't have access to a Mac. You can't download your whole library from the online environment, there's a 1000 image limit per shot.
edit: Also I have not found a good way to export from Apple Notes so I have a habit of typing into .md files from the terminal.
edit2: Gave it a search and tried Exporter. Duh. Works great!
Actually an anecdote on switching, my father in law bought an iPhone in a pawn shop. It was logged in with someone else’s iCloud account. He just used that until he dropped dead. We had no idea until I had to clean his phone out. My mother doesn’t even know what iCloud is. Literally total ignorance must be the default for everyone these days.
I’ve done the random switch thing as well as a test case. But to Microsoft. It took me a day to export all photos from Photos.app and into OneDrive and that was with a Mac (105Gb). And of course you lose all the edits you did if you export the originals.
I have an unhealthy habit of switching between FOSS and Apple a few times a year (don't ask) and generally it is pretty easy. The most annoying thing to me is Photos export, especially if you don't have access to a Mac. You can't download your whole library from the online environment, there's a 1000 image limit per shot.
edit: Also I have not found a good way to export from Apple Notes so I have a habit of typing into .md files from the terminal.
edit2: Gave it a search and tried Exporter. Duh. Works great!