Yes, I forgot about Parsec, that's a good suggestion. I remember trying it, and not getting it to do what I want, unfortunately I don't remember why. I think I was stuck in the "Arcade", when all I wanted was to share my desktop or one window. It certainly looks like exactly what I was looking for.
Arcade is like a quick match menu for finding a game to play.
You can share any screen or desktop from the main app and have friends connect
Parsec looks great, but I'd be grateful for metrics (bc who knows what "low-latency" really means).
In home streaming with Parsec for me with a MoCA/Ethernet connection typically has 1-2ms of network latency. Over wifi in-home is more, closer to 20-30ms with a mediocre laptop wifi card. Playing online with my brother who lives 35 miles away using an Ethernet connection I typically see 15-25ms latency, not much worse than a 'meh' bluetooth controller. It's likely worth noting that my brother and I both have the same cable internet provider, but we also sometimes play with my brother-in-law who lives another 40 miles from me (~60 miles from my brother) and we can all play games like Streets of Rogue together from my brother's PC without issue.
Wow, that is better than I'd hoped! Thanks so much for your response! (I know it's just an anecdote, but bc I'm looking to see what it's perf limits might be, even one data point like this is very helpful.)