I sympathize. It is probably the most difficult ecosystem to get out of. Nextcloud was one of the most important pieces of software for some I know who got off of Apple. You can setup your own private cloud or use a community server you trust to replace pretty much everything on Icloud: Files, photos, music, notes, tasks, contacts, calendar, passwords, bookmarks, facetime, and many more. Migrate everything there, and then you can switch to any operating systems you want.