I'll describe why it doesn't work, then we can look for solutions.

On day view, if you click on Tag timeline to select it, then write filter at the bottom, it will also filter on notes. Same is true for Advanced search.

We removed it from Timesheet because notes are not necessarily displayed. If they are not, then it is not clear why some tags appear among results. For example I could have
'Tag1' with note 'this is a note'

If I filter on 'note', then tag1 will be among the results, but if notes are not displayed it is not clear why it is there.

Possible things we could do:
- filter also on notes when they are displayed
- we could have two boxes, filter tags and filter notes.
- or some syntax for filter, like 'tag1 notes:note'.

What do you think?