Attempt to get recently changed filtering working

See the setup above.
Files changed less that a week ago are not displayed with a bold font.

What else do I need to set to get the filer working?

Fortunately I found the reason where the problem is. It appears that the filter is working fine, the problem is within the fond used to render the File display.
I had it on "Segoe UI Semibold" which makes for a nicely legible font. Unfortunately, there is no bold variant of the Semibold font, so the change to Bold, as forced by the filter has no effect. It also is not possible to change the font for a specific label.

Two solutions: change the File font to something else, or select a label that change other chracteristics like italic, underline or color

You may have problems when you create more labels (different colors for different file types and/or "modified within.." as in your case, plus some more). These filters will start override each other.
For "modified within.." you should tbone's script:
[url]Column: ModifiedWithin (alternative to 'modified'-labels)]

It works perfect. On the picture below you can see some filters "in action" (bold is for folders, colors for file types) - and one additional column (small square) indicating "modified within" files.