I remember there being apps like xender, easy share etc. which lets you share files by one person activating hotspot and the other wifi you just have to have both party close to each other and they use no data . But they are all closed source and probably spyware and its too much of a hassle to get others to download a file sharing app from fdroid when you need to share big files so is there any website or web app which is private (completely offline after loading, is foss etc.). It also has to work on android and have good enough speed .
Perhaps sharedrop would be best suited for you?
https://www.sharedrop.io/
No vpn ? Why does it use data ?
Sorry, I don’t ubderstand your question. As far as I know, sharedrop works in the local network, doesn’t it?
I think they’re asking about the text on the website that says “not compatible with VPNs” which I think is a reference to an Android system limitation where you simply must turn off an existing VPN connection to use the app merely because it interferes with the app becoming its own localhost VPN to get around android networking limitations.