Is it okay to change niche completely?

Domain was used for something else before. Is it okay to change niche completely?

nope, google will penalize it for sure....

Now, if you don't care about google (which - in my opinion - you shouldn't) you can obviously do with the domain whatever you like, maybe Bing and other SEs won't care

You can change niche completely, but niche match still matters in my experience. A relevant history usually feels more natural and can make the transition smoother. If you're looking for aged domains, NakamaID has options across different niches, so it's easier to find something closer to what you actually need.