If I have $300-500 that I want to use for ETFs, is there a hot ETF / Index fund I should choose?

Hi- I barely know what I’m doing but I just got a bonus and I want to invest $300-500 in my brokerage. I have a 401k, Roth, and HYS- as well as a brokerage account in the S&P 500. I am thinking of doing the Bogelhead 3 fund portfolio but keep seeing things about Palantir. Should I invest in an individual stock? Please give me tips I’m so lost