Ultimately, you have to store the file somewhere and sync it to all the places you want it. The magic here is that it decouples the "password manager" and the "file syncer" so you can (and should) use whatever you're already using. Greenfield, Nextcloud is the cleanest if you want FOSS and self-hosting (and they have clients for basically every platform under the sun), otherwise pick your poison between google drive, dropbox, icloud, onedrive, etc.