In Quicken, you could ignore the fact that you have Fidelity Govt Cash and set up the account for a linked checking account. To get started, you would manually enter a Sell in Quicken for the balance of your Fidelity Govt Cash. Back up your data file first in case the result is not to your liking.If you do this, you will have to not accept the Buys and Sells for Fidelity Govt Cash that Fidelity downloads, and change ReinvDivs to Divs when it pays interest. Also at the end of each download session, Quicken may complain that the downloaded balance of FDRXX does not match the balance in Quicken.
Didn't Fidelity require you to change from FDRXX to SPAXX due to a federal requirement. SPAXX can automatically be set up as a checking account. I have it, I did it, No problem.