TOMB5 VS Spring RTS game engine

Tomb Raider: Chronicles (Completed ?)

TOMB5 - Tomb Raider: Chronicles

Seems the support would be a realistic feature, though, because it's based on https://springrts.com/ that does support MacOS X.

springrts: Designed for 3D rts games. May be worth looking into if that's what you're making. The site is kind of lack luster so I didn't do too much digging around.

...or Total Annihilation Spring, nowadays known as Spring RTS: https://springrts.com/

My current favorite is Beyond All Reason. Before BAR, my favorite was Zero-K. Both BAR and zk use the same game engine, SpringRTS. BAR and zk are very similar to one another, and they're successors for Total Annihilation and Supreme Commander.

Obligatory mention of another open source RTS engine (lineage tracing back to the original Total Annihilation): https://springrts.com/

The other thing is that if you're going to make an engine focused on rts games, you should probably study an existing RTS-focused engine. For example, here's the source code for Spring. Learn what it does, why, and how. You might decide this is good enough for what you want to do. You might decide this is pretty close, and you'll only want to extend it rather than start from scratch. You might decide to still start from scratch, but at least you learned something about requirements/ methods/ etc.

Pretty much any game on the Spring Engine (which Zero-K is on) will work on Linux.

That said, having that many units will be very challenging in pretty much any general purpose engine and you may want to consider an engine built specifically for RTS games. A quick search found the spring RTS engine: https://springrts.com/

Total Annihilation RTS. Really impressive for the hardware at the time, moddable, and super fun. The community has made SpringRTS and Beyond all Reason and last I heard Cavdog was essentially sold ~4 times and the original source code was lost. I still find the intro impressive considering it was released in 1997.