The PS5 system software was recently updated and will pester you to update your controller if you are using the FGC2.
Brook has put out a new update for the FGC2 to fix this, but it is not yet available using their normal firmware updating software.
They published a website that allows updating the FGC2 firmware through the browser without downloading and installing a program. It only works with Google Chrome or Brave on a Windows or Mac desktop.
The FGC2 must be plugged into the computer while squeezing the two switches on the sides,

then select the Wingman Series,
click on the Connect button, then grant permission for the browser to access the HID device WPM USB.
Select WPM USB and Connect.
Pick the most recent firmware in the list:
Click Start and wait for the update to finish. The lights on the FGC2 will flash then a message will pop up: