I've been working with this issue for along time. Trying to find something platform agnostic and works with vpns.
App wise, I suggest Localsend for files
Information wise, I suggest Saladroom although there are several alternatives as well like ToffeeShare and ShareDrop
I mostly use Signal though, as it's the simplest at hand app which fairly reliably makes it accessible to my various devices... With the downside of storing it.