Hi @RemonK, welcome to the forums. In the match setup hit "Player" then you can make your selection.

How do i add more players in singleplayer mode??

make sense, didn't check seleucids bonus

The hardest to compile is Spidermonkey 38 mainly because it relies on python 2. Spidermonkey has very few minor versions that are ABI (backward compatible) sometimes they even break it in minor like 76.3 and .5

I didn't really forget that. I've just assumed that those library versions were backwards-compatible (as they should be) and that he would need fewer libraries anyway since it's an older alpha release.  But yes, that is one issue you inevitably hit while learning to compile. And this knowledge ia quite valuable in today's world.