You could set up an "on app launch" automation shortcut for Maps to alter the Color Filter setting, but I'm not sure how you'd automate switching it back after closing/leaving Maps. I don't use the automations, but instead have a shortcuts widget with "toggle greyscreen" (among others) which is sufficient for me most of the time.

You can have 2 automation, one which enable grayscale when certain apps are open and one that disable it when the apps are closed. It’s under shortcuts > automation > app > is closed.

I put this in a different comment but you can also have a single automation that toggles the setting for those apps on open and close. This way you have a single list of apps to maintain.