The Steam Game Festival: February 2021 will run from February 3, 2021 until February 9, 2021.
Devs are encouraged to enter demos of their unlreleased games into the festival until December 2, 2020.
You are eligible to participate if your title is due out within six months after the festival (between February 10, 2021 and September 1, 2021).
The Steam Game Festival is a multi-day celebration where fans can try out demos, chat with developers, watch live streams, and learn about upcoming games on Steam. For developers, the Steam Game Festival is an opportunity to get early feedback from players and build an audience for a future launch on Steam.
Valve
More information is available here.