Here's another photo. Also I water it roughly once a week, and always make sure the soil is dry (at least near the surface) before watering it again.

I'm not very familiar with cactus care, but it looks like it could be pest damage??? another thing you could do is pull it out and check for root health (wrap a towel around the cactus a couple times), as the soil it's currently in looks quite water retentive.

I am big into cactus so I should know the plant u have is a hamatocactus I wouldn't be worried about the yellow spots that spices has many different colors there's just one thing be sure it's not rot and pull it out of the ground and check roots