It's pretty obvious to people who speak 2+ language that there are trade-offs between "going deep" in one language and having "surface-level" knowledge of many languages.
The one thing they found which bilinguals might be better at has to do with digit recall, which actually agrees with previous research that bilinguals are 'more logical' in their second tongue and 'more emotional' in their native tongue.
https://news.uchicago.edu/story/communicating-foreign-langua...
https://psycnet.apa.org/record/2006-02935-000
https://www.languagemagazine.com/2023/04/21/bilinguals-react....
So the results may have been different if each participant was allowed to take the test in their mother tongue.
The list of things they tested is way too small to conclude that there are no general cognitive advantages. What is "general" anyway?
Things they didn't test:
- the ability to learn new languages
- the ability to guess the meaning of unfamiliar words from context clues
- ability to communicate or get by in a brand new/unfamiliar environment
- ability to detect BS (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8423309/)
- ability to improvise
- abstract thinking (not being limited by a linear inner voice)
- etc...
There are many confounding factors they didn't test for. e.g., what if the bilinguals are more logical, but have weaker comprehension of the question? do those things cancel out? Or, if being multilingual makes you "overthink" prompts and maybe you get penalized on time in standardized tests, etc...
According to their questionnaire, the "bilingualness" of participants was self-reported, all you had to do was enter a number between 1 and 20 for the number of languages you speak.. It would have been better if written and spoken proficiency in each of the second languages had been tested and used to correlate with the results.
I could go on. I think this is actually one of the worst studies I've ever read in terms of "confidence of the title" vs. "what they actually tested."