The problem is the plastic that doesn't make it landfill and is instead in the ocean/rest of the environment
So tossing plastic in the recycle bin is plausibly an environmental net negative.
If you put it in landfill in the US, it’s definitely in landfill. If you “recycle” it, it may get shipped to China (or now Cambodia) and then dumped somewhere.
[0] https://www.mdpi.com/2076-3298/7/10/73/htm indicates that a lot of the coastal debris is plastic bags, while a lot of the offshore debris is fishing nets
https://www.youtube.com/watch?v=yYMuh-5V9fk
Portions of that garbage will eventually make it to an ocean. Especially plastics due to the simple fact that it floats.
So that’s more of a reason to just discard plastic.