The next Steam Next Fest will run from October 3 - October 10, 2022. These fests usually pop up multiple times a year, and the last one ran from June 13, 2022 to June 30, 2022.
Steam Festivals (now called Next Fest) aren't sales, exactly, but they're another way to play games for cheap. Since 2020, Steam has been running regular festival weeks where hundreds of upcoming games offer free demos for you to play. It can be a daunting list to sort through, like sales are, but it's a great way to try something you've had your eye on.