syncthing to sync your notes folder (and your pictures, audiobooks, whatevers); then the editors can be anything, i.e. whatever you prefer on each platform. sync over the internet can be disabled and set so it works only on your home LAN. also, sync direction, maybe you want it to sync only one way. turn on versioning to get at the version from two weeks ago. etc.
you should be in the know by now to not get locked in by any one provider or app. always go with the thing that gives you exit options.
