Windows based Freeflow webui should be admin <lower case> for the System Administrator account in the dropdown.
The Windows password on it is service! when logging in locally on the FFPS itself <or when you remote desktop into it>
Dependant on the Version of FFPS, it may have the bug that was fixed a long while back where the default password was set to expire by default.
Have you tried multiple web browsers?
There have been no updates to address the 2020 California Password law (SB-327) that I have been made aware of, but if there has been, Gabiene's suggestion is probably correct
Have you tried the Serial Number of the FreeFlow?
Can any one chimne in on the New Web Ui Password for the FreeFlow server
I tried user "admin" and password "administ" as well as "service!" but I belive this has changed after EFI took over