There's a few things to factor in.

First, your employer is very likely only going to allow contributions from your paycheck to go to this provider. Paycheck contributions are the most effective way to get money into an HSA because those dollars bypass payroll taxes. Saving on your owed income tax can be done by deducting non-payroll contributions on your return, but that method cannot get you the 7.5% payroll tax savings.

Second is that you are allowed to transfer your HSA balance from this provider to any other provider you've opened an HSA at. So you could find a new provider without the investment fee (Lively and Fidelity are common recommendations) and use that as your primary HSA investment account.

The last thing is that every HSA provider I've ever had charged a $25-35 transfer fee to send my balance to another HSA. So now you have to balance that against the monthly fee or leaving your balance un-invested for longer. The IRS does allow an "indirect HSA rollover" that bypasses that fee, but you only get to do that once every 12 months.

So there are ways to get out of that fee vs. costs incurred vs. investment goals that you have to balance. One simple strategy would be to just accumulate cash in this employer HSA (no fee), then use your "once per 12 month" indirect rollover to push that cash to another HSA where you do all your investing.