Throughout the 17 months it has been available, the Xbox Series X|S has outsold the Xbox 360 by nearly 4.5 million units throughout that same 17 month period. This is according to VGChartz, which has released its March sales reports as well as a sales comparison article for the two consoles.
The article notes that both the Series X|S and the Xbox 360 released in the month of November, so the initial holiday season launch lines up for both systems as a fair comparison. As of March 2022 Microsoft's ninth generation console(s) has sold 13.87 million units. It currently is ahead of comparative Xbox 360 sells by 4.49 million units, a gap which has widened by nearly half a million (480,485) units since the previous month.
By comparison, the Xbox 360 had sold 9.38 million units after 17 months on the market. The 360 didn't reach the 10 million units sold mark until its 19th month, and it wasn't until the 360 had been on shelves for 26 months until it reached the sales number currently held by the Series X|S.
Why does any of this matter? While the 360's successor, the Xbox One, is now seen as a misstep by Microsoft thanks to its less-than-stellar reveal and messaging that was seen as "anti-gamer," the Xbox 360 was an important success for Microsoft that resonated with the more than 85 million gamers who wound up buying the system. The Series X|S represents a return to form and a chance for the company to redeem itself for its 8th generation mistakes, at least in the eyes of gamers. This is why so much attention is being paid to these sales figures.
Of course one has to take into account the fact that the home video game console market is a much bigger pie today than it was in 2005, which does undercut some of the Series X|S success relative to that of the Xbox 360 in that it has a bigger piece of what is a much bigger market.