vidsgame: I had that problem recently with Redout being on sale and it said no deadline. I had to

Go to the home page.

Scroll down to the bottom.

Where it said news, I looked for Redout or whatever game you're specifically looking for.
Redout was released on GOG recently so those titles usually go like "Release: Redout Solar Edition"

Clicking on the article showed that the sale was going to end on the 6th of December.

I know it's a bit involved but that's how it goes now for some games, especially releases sometimes because the weekly and weekend sales seem to have it differently and their own pages and News articles as well. It can get confusing.