I think tidally locked planets are fascinating. If they have water, they could be eyeball planets. There’s a habitable ring in the twilight zone, and depending on how hot the day side is parts of that might be habitable too.
But we’ll likely run into the same issue re the atmosphere as we have with Mars: no magnetosphere to prevent any atmosphere from getting stripped away. It’s starting to look like a self-protecting atmosphere like Earth has is quite rare in rocky planets.
If I could summon a genie and learn any one bit of knowledge, it’d be how to restart Mars’s dynamo. Once we have that, terraforming is a solved problem. Not easy, but doable.