One of the many reviews, can't recall exactly which one, said the first day they had around 300 and then over the weekend they were well over 500 for them to look at. The review also mentioned if there was any game in particular they were interested in using to let Xbox know and they'll get it on the approved list.
Ars said the list was some 1000 games on 2020-09-28:
No, I didn’t get to all 1,000 games, sorry
The answer I eventually got was, "Sure, we'll call your bluff." Today, I've been given the greenlight to talk about the console's current backward-compatibility testing phase, and Microsoft has had zero control of my tests or takeaways—other than limiting me to 1,000 games across every existing Xbox platform. While the program will eventually encompass every game that works on Xbox One consoles, the pre-release compatibility list is a bit more narrow. 1,000 is a big number, but it leaves some huge Xbox hits out of my testing.
