I don’t know how long this will last, but I started doing this recently with Vanguard’s VUSXX (short-term Treasury) fund when I realized it had significantly higher after-tax yield than high-interest savings accounts without the hassle of manually rolling over T-bills, and it looks like many other people have been moving in this direction.
If you buy t-bills yourself fees are low, and brokers aren't banks - so risk of money being stuck there is low.
It's a bit of work but very manageable. 10/10 recommend, you earn more than a savings account.
Fees on buying treasuries are zero if you buy them directly from the treasury or any of the large brokers (Vanguard, Fidelity, etc).