I know there are regional restrictions that prevent certain items from appearing in restricted countries, but in general, how to calculate the number of games which you could go through if you browse through all the items in the Discovery Queue?
The only people that know what's going to be in the discovery queue, are the programmers who designed it. But... We can figure out how many games, apps, and videos there are in general.
Simply go this link: https://store.steampowered.com/search/?sort_by=Released_DESC&category1=998
You'll notice that no tags are checked and selected type is: Games
At the bottom left it shows (currently) showing 1 - 25 of 29799
Software (currently): showing 1 - 25 of 771
Videos (currently): showing 1 - 25 of 367
Total Items on steam: 53404