Sales have worked for this same game in the past but suddenly this one doesn't seem to work.
I've had this sale ready to go for weeks and it looks fine if you go directly to the sale page: https://itch.io/s/117276/cosmic-misfit-anniversary-sale It shows a "Buy for" discount button, although when you click it, it seems to still require the full price, not the sale price.
Similarly, the regular store page shows the full price only and no indication of the active sale.
Note: I did see this issue from a few years back and wonder if there's been progress on it but didn't want to resurrect an old post to find out: https://itch.io/t/662169/sale-not-showing-up-on-game-pages