How should I make a tidally locked planet have a spot on its surface?

@FriendlyFin Thanks for the tip, I'll try that.

if you want something more barren, like mercury, disable the ocean and make the entire planet a reddish color according to the star it orbits, in this case an M class star (red dwarf) while keeping the custom map

It depends on what planet template you’re using
if you’re using a “terrestrial” template, go to the planet brush map and create a large circular shape in the “continents” map, then go to terrain generation and turn off ignore map for the continents element