My suggestions are all open-source, and therefore free forever.
Beyond All Reason is an amazing RTS. I’ve heard people say it’s one of the best RTS in existence, but I haven’t played any other RTS myself, so I can’t verify that.
Space Station 14, a remake/continuation of Space Station 13, is a top-down multiplayer role-playing game. I like to describe it as “Among Us but in way more complicated”, but it is sooo much more than that. The learning curve is steep, and rounds usually go for at least an hour, but if you want to try out new stuff, give it a go. In my experience, the community is really welcoming of new players.
SuperTuxKart is arguably the definitive open-source MarioCart clone.
It would (hopefully) have less attack surface. Electron is, after all, a whole browser, and needs to be able to do all the things a browser can do, while a native implementation can limit itself to just the very limited network interactions needed. (e.g. while XSS attacks are quite hard to do on a modern browser, a native app would make them impossible)