The teaser image doesn't offer much in the way of hints as to what might be revealed on the date, but it does include a green painted stripe on a wall that looks a bit worn... A caption is also included "We scoured the earth, looking for salvation...".
This tease was posted by the Twitter account for the Rainbow Six franchise so it could be related to new content for Rainbow Six Siege, such as a seasonal event. In fact, it might even be related to the Rainbow Six Siege Apocalypse event which leaked recently. Based on the caption, this seems like the most likely reveal.
This tease could also be for the reveal of Rainbow Six Quarantine, Ubisoft's PvE take on the tactical gameplay of Siege.
Rainbow Six Quarantine was originally announced back at E3 2019 but hasn't been seen since then. Earlier this year, some key art and the new name for the game (Rainbow Six Parasite) leaked via the PlayStation Network, alongside more than an hour of gameplay on the internet, although Ubisoft later said these assets were temporary and that more details would be revealed later this year.
Information about Rainbox Six Parasite is scarce right now, but you can see a recap of everything we know about it here.
In other Rainbow Six Siege news, a new Rick and Morty bundle is now available to buy, whilst an AbleGamers collaboration for the game has raised more than $170,000.