If this E3 is just like the one from 2019, that lasted about the same this one will last, we can expect something similar, and there we had:
-12 trailers from Nintendo (8 from games for 2021, all of them already known, 2 Smash DLC's and 2 for games post 2021)
-10 trailers from third parties (I'd say half of them for important titles, the other half was kind of filler, most of the trailers were like a minute long though)
If it's something like that Nintendo already has like 6 things that most likely will be there (the 2 Pokémon games, BOTW2, Splatoon 3, Hyrule Warriors and Smash DLC), so unless there are less third party trailers, it's probably going to be around 6 trailers for unknown stuff, and among them could be AC:NH DLC, Pokémon Unite, Cruis'n Blast and maybe a second Smash DLC, so probably it's most likely we'll see at most 3 or 4 new games