I'd find a few people that have been at startups of a similar size and stage and talk to them about this.

First, there is no single "startup" definition. Are you the third employee, did they just raise series A, are they nearing IPO or acquisition?

From my own experience - hire during scaling post series A, expect more disorganization than you're used to at an established company, more decisions and direction based on how well you can argue them instead of actual evidence from the market, more changes in direction, overall more chaos. It can be a lot of fun, but if you are not in the company's inner circle, you have to go with the flow a lot more and accept things will change all the time for reasons you have no control over, and product features or deals you worked on can often get scrapped after you put a lot of effort into them.

That was a bit of a rant, I liked working at a startup, but it was much more chaotic with literally nobody knowing what they were doing than I expected. On the other hand, if you're there in a high growth phase, there is lots of optimism, lots of fun, lots of learning and social connection