I was playing minecraft on normal and exploring the world at night when I noticed that there was way more mobs than it used to have, also I made a house in a plain creative world and in less then a minute it was infested with hostile mobs, As I said before I was playing in normal mode, I also tested in easy and the same thing happened.
My survival word was made in 1.14 and passed to 1.15 and now 1.16, it only happens when I generate new terrain, but in the flat world anywhere I build something closed the mobs spawn too much
I havent noticed anything weird with neutral or pacific mobs
The example with the flat world is of course expected to spawn a lot of mobs, since they have nowhere else to spawn. As for your experience in your survival world, it can occasionally occur that they spawn more than other times, that is just the random chance part of spawning.