https://www.fsarchiver.org/quickstart/ It’s faster and more efficient than just dd :)

WG Tunnel does that natively, you can whitelist some wifis and auto connect on other and optionally on mobile data

For me: uploading single file using their client ~25MB/s, downloading ~50MB/s (30-60MB/s). In newer versions of their linux client it’s possible to mount filen as network drive or to start webdav/s3 server.