That would be the gambler’s fallacy. While it is true that the collective probability increases as you do more encounters, it is erroneous to believe that this affects the probability of a single encounter in any way. That sentence is very confusing, so let me give an example.
If you were to be given 4096 Pokémon all at once, each with a 1/4096 chance of being shiny, before you went to check them, there would be a ~63% collective chance of there being at least one shiny among them. But probability is caused by uncertainty, so as you check each one, its individual 1/4096 chance becomes either 0 or 100%, because now you know, so that Pokémon’s chance must be subtracted from the collective total. If you go through 4095 of them without finding a shiny, the 4096th one doesn’t suddenly jump up to a 63% chance, it’s exactly the same as the first one. Whenever you’re hunting with fixed odds (full odds, Charm odds, MM, etc.; anything that doesn’t actually change the odds over time like various chaining methods), it’s best to think of every single encounter as exactly the same as the first one in terms of probability (because it is).
I hope I explained that well.