You could hook up a Mac to the internet in 1985-ish, transferring files using telnet.
Mac OS still ships with BinHex (https://en.m.wikipedia.org/wiki/BinHex), I think, so for Macs, that might already be the simplest way to exchange data between an early Mac and a modern machine (even if you have a floppy drive, does it read Mac disks?)
Edit: maybe my memory is of, and it was direct dial-up to another machine, not across the internet. NCSA Telnet (https://en.wikipedia.org/wiki/NCSA_Telnet) supported TCP/IP before the OS did (yes, that was possible. I don’t know whether you still could do that on a modern system), though, so who knows?