There are many articles, I tend to distrust articles used as marketing.
https://www.sciencedirect.com/science/article/pii/S2666682022000123
Many articles like the linked one back these results. That said, submerging in water for a month will change a lot of materials, hardly practical.
Vapours, heat, water all change PLA. In your short sample it easily could have been effected by something else. PLA has low resistance to many acids, acetic, nitric, even citric and many solvents and alcohols. It is also possible that the filament was exposed to VOCs and these too cause the same kind of issues.
I have tried to use PLA around a handful of chemicals, acetic, and oxidizers and parts became brittle in days and crumble apart.
I personally have PLA parts outside for years, it is discoloured but not completely brittle, my soap dish, the first design I did has been used daily for 5 or 6 years it too is not more brittle then a newly printed one.
Personally I suspect PLA brittle filaments are not only water but something else too. Removing the first few wraps seems to resolve the issue for me.
If PLA became really brittle exposed to some water vapour in the air quickly. Parts made with it would be useless, this would be a huge issue and the industry would move away from it.
My experience I have never seen PLA degrade noticeably exposed to only water. Maybe your experience is different.