There have been studies, and I know this also anecdotally from native speakers, that e.g. "business English", at least in non-English countries, becomes its own, more restrictive variant of English because of the high percentage of non-native speakers. I know that some such native speakers have said that they feel their English got worse after living abroad for a while.

Of course, overall, this is a very slow process. People don't stop applying the rules or simplify vocabulary over night or even within the span of a couple of years, but there is growing evidence in general that the more speakers a language has, the more it tends to simplify structurally, e.g. https://royalsocietypublishing.org/doi/10.1098/rsos.181274