If those games can do LAN connections (computers on the same network), you could use something like Hamachi to put your computers on a virtual network together. I'm sure there are more modern versions of Hamachi, but that's how I used to do it in the early 2010s.

For all their faults they don't use kernel level anti cheat. Both StarCraft 1 and 2 are free. StarCraft 1 should at least have LAN play.

I'm playing Age of empires 2 definitive edition from Steam and it's an awesome modernized RTS experience

Parsec is probably what you need. Me and my brother played through BG1 (for ps2 I believe) with an emulator and parsec. For the most part there was no lag. We simulated us both playing on his computer the same way you would play couch co-op, just in different areas.

I cant help you with RTS games, but u should def try old wow private servers. My recommendation is Turtle-wow . Its old school wow with tons of players aaand because its old, every pc can run it.