OP said they don’t want to pay for Hue.

Yup, that’s a pain I’m the butt to deal with.

Where is that permission, I don’t see it in the Permission Manager on my Pixel 8?

I read somewhere, the suggestion, that the filter be replaced when air flow has reduced by 50% from when the filter is new. IDK, that seems reasonable to me and should be measurable.

I have always replaced filters on a schedule, but it has always felt wasteful. Sometimes the filter is clearly dirty and sometimes it is not. I would like something more specific.

I will look into PMS7003.