Today's example: Unreal Tournament GOTY - normal price: $9.99, current promo price: $1.99.

When I set "price" filter to "under $5" I can't see this game on the list - why?

The price filter usually takes into consideration the normal price, not the discounted one, or at least it's always been like that in my experience.

Sigh. Filters already lack many options (like setting my own personal price level to show all games below it) but it seems this situation is even worse than I thought.

There are quite a few bugs like that around here.

For example, the last 3 DLC releases...
Warhammer 40,000: Sanctus Reach - Horrors of the Warp
Pillars of Eternity II: Deadfire - Rum Runner’s Pack
Pillars of Eternity II: Deadfire - Soundtrack

While they link fine from the news posts, you can't search for them in the "Store" and they do not add to the store title count.

Then there is the "On Sale Now" store feature...
But when I checked, the THQ/Nordic games aren't listed.
(And there are more THQ/Nordic games on sale than the rest of the catalog!)