under fidelity FBTC the OP does not own a share of BTC
he owns a share of a fidelity company share. he cannot redeem that share for actual BTC. he has no ownership rights of actual BTC

however yes using the 401k method to own shares EXPOSED to bitcoin PRICE. means he gets the exact same ups-down of the market movements, with for him the upside that he can purchase exposure amounts at a discount due to pre-tax share purchasing. and tax free selling of shares

but its still worth stating the OP does not have ownership rights over actual bitcoin.