The Activity Details report filter is missing the 'Tags' filter. The last filter is 'Groups' and just before that is 'County' which is where 'Tags' should be. The criteria for this field is 'Is one of' and the selection hint is 'Choose state first' - and is unselectable. The previous criteria to that is also 'County' which is working OK. This is a UK installation, at 5.26.2 and I have another installation at this same level where the 'Tag' filter shows OK. Very odd - I've disabled extensions, checked localisation, settings etc etc. I upgraded to 5.27.3 but exactly the same.
Only bare tags (tags not part of an activity set) trigger the field to appear.
I think the report should be updated to match how it's done elsewhere. Where I've seen it it's usually done as two separate fields.