Reddit user swine_flu_greg posted a wealth of information on 2K's upcoming game reveals that has been since verified by Jason Schreier, though the Bloomberg reporter also said he's not sure all of these titles will be revealed at E3 2021.
We already knew that Gearbox would be unveiling a new franchise at their conference, to be released in 2K's fiscal year 2022. It looks that's going to be a Borderlands spin-off titled either Tiny Tina's Wonderlands or just Wonderlands.
Wonderlands: Codename Daffodil - It's a Borderlands spin-off title featuring Tiny Tina. The final name could also be "Tiny Tina's Wonderlands" (as this is the name that Gearbox already trademarked.) Seems to be the same style as all other Borderlands games with "Multiclass-Heroes" to play as. This spin-off is rumoured since last year, so I guess this isn't really new. Reveal should be expected at E3. EDIT: Here's the trademark for Wonderlands.
We also knew that Firaxis would be announcing a new game. According to the leaker, this will be an XCOM-like title set in the Marvel universe.
New Firaxis Game: Codename CODA - New turn-based action game using Marvel property. Source described it as "XCOM with Marvel heroes". Seems like some famous actors are voicing the characters.
Last but certainly not least, there's also some info on Hangar 13's new game, which is described as 'Cthulhu meets Saints Row'. This doesn't sound like it'll be released any time soon, though.
Codename Volt: New action game, seems to be in really early development. Logo looks similar to the Fallout-Logo. No final name yet. Source described it as "Cthulhu meets Saints Row". Game looked pretty unfinished in the trailer. Sadly, my source didn't know which studio is developing this title. I think it could be Hangar13, as they had a leaked contract last year that stated that they are working on a "open-world sci-fi title with supernatural elements".
NBA 2K22 will reportedly feature Dirk Nowitzki on the cover, though that might be some kind of Legend Edition rather than the regular one.