On the contrary the beneficial properties are popularly ascribed to bilingualism itself.

For example:

https://www.nytimes.com/2012/03/18/opinion/sunday/the-benefi...?

https://www.wsj.com/articles/does-being-bilingual-make-you-s...

Although it seems that skepticism about this truism goes back a few years as well.

https://journals.sagepub.com/doi/10.1177/0956797614557866