@awalker
Please consider changing your Logic to the following:
Two dropdowns - start and end range dropdowns. ddRangeStart and ddRangeEnd
Set the Items property of both to: ForAll(Sequence(26, 0), {Char:Char(65+Value), Value:65+Value})
Set the OnChange action of both to:
UpdateContext({range: ForAll(Sequence(ddRangeEnd.Selected.Value - ddRangeStart.Selected.Value +1), Char(Self.Selected.Value + Value-1))})
For the Items property of your Gallery, add to your existing formula this:
Filter(
AddColumns(
<yourExistingItemsPropertyFormulaHere>,
"Char", Left(Title, 1)
),
IsBlank(range) ||
Char in range
)
This should give you what you are looking for.
I hope this is helpful for you.