Buy GBTC with money in within Fidelity HSA (health savings acc)?

I have a 401k and an HSA with Fidelity through my employer. Each pay period, they contribute to my 401k. Every 3 months, they add a small amount of money ($125) into my HSA. The 401k and HSA are two different accounts.

When I try to "trade" with Fidelity, it does not allow me to do it with the 401k. With the 401k, there are a limited number of options to choose. I cannot find out how to invest in individual stocks in the 401k. It was all just target date funds, SP500, total market index, etc. So my 401k is just SP500.

However, it does allow me to "trade" (buy) stocks and GBTC under my HSA acc.

I was thinking, should I just use that to buy GBTC? It's only $125 every 3 months so it's really insignificant. It's probably just a waste of time to even think about this in the first place. We are talking about $500 in a whole year lol