It’s possible to create a (greyscale) color filter toggle, as well as time based or app open/close activation with the iOS “shortcuts” automation: https://m.youtube.com/watch?v=W32pf_97onM
>>Modifi+(OP)
didn’t open the video, but you can also set double or triple tap on back of your iphone shortcut for this. i have a red filter set up for late night doom scrolling