So this isn't a question, it's a bit of a workaround I came up when wanting to filter a gallery using a dropdown.
The main problem faced was how to disable the filter, as in give the option to the user to turn the filter on and off. The easiest way I've found is as below.
Filter(collection, item_id=item_id*!toggle. Value+dropdown.selected.item_id*toggle.value).
How the above works is when the toggle is set to off, the item_id is set equal to item_id, and as such all the records are shown. If it's set to on, item_id is set to equal the selection of the dropdown, voila!
There's a couple of caveats, essentially if there are records that the item_id is set to 0 or blank then these show up whether is filter is enabled or not.
On the other hand, the coding is very streamlined and there's no delegation warnings with this method (so I assume that the formula is delegable).
That's all.