KSP 2 is the one they're (or were) very actively developing, but that has been in disarray, to say the least.

They released it with basically none of the promised content, at this point, people report it feels like KSP 1 but worse, with visual mods, and KSP 1 with mods is said to be much better.

In my personal experience, KSP 1 was perfectly fine and didnt need a sequel, building ontop of the existing fanbase, engine, mods and knowledge would have been smart.

Porting KSP 1 to a newer unity version, the new rendering system, and really focusing in on the modding even more, providing more tools etc. would have been very smart.

Now KSP 2 has been in no-mans-sky promise land forever, people are refunding iz, its generally a clusterfuck.

For more info, check out the subreddit r/kerbalspaceprogram