I have an account at Marcus also. When they first launched, they limited the maximum balance. Not sure if they still do. Barclays offers a similar product. But nowadays plain old T-bills pay 2% and they're state-tax free. I also have a fair amount in munis, single issues and closed-end funds. Recently bought more as they cheapened on the bond selloff. But they aren't riskless, of course.
Mine is at Vanguard muni money market fund. SEC yield is 1.55%, after tax yield is much better than most of the bank rates like (Marcus, Capital one etc). Even their Prime money market pays 1.81%