How can you see how many people play a game on steam?

steam does have its own charts page under the store menu that shows the most played games right now with player counts. it only lists the top ones though, so for anything smaller you're back to steamdb.

steam doesn't show it on the store page. SteamDB and Steam Charts both show the current players plus a graph over time and the all time peak. just search the game's name on either one. keep in mind that's steam only, so a game that's also on game pass or the epic store has more players than it shows.