Work at YC startup as new grad?

I got messaged twice by two different founders on YC’s WaaS site for a founding engineer position. As someone with no swe experience (past internships were ml/data science, more research based), would working at a startup help/force me to learn swe fundamentals? Is the work/life balance really that bad? What red flags should I be looking out for? For context, these are small pre-seed startups with fewer than 10 employees.

I have very few interviews left for swe new grad and I’m waiting for interview results for a FAANG (which I’m assuming Im getting rejected from) so I may actually have to consider one of these startups as an option, since it’s better than nothing I suppose. I’m just a bit wary of companies entrusting much of their core product to grads with zero experience.