Besides structure prediction, Foldit is used for the inverse problem: protein design.
Considering the resource requirements for this AI approach mentioned in the article, its unlikely that its been tested on more than a few tens to hundreds of proteins. This may only work on a subset of the proteome so I would think it worth it to continue playing if you find it to be a fun past-time.
Those were the requirements for training it.
Yes, no point, as far as I understand it.
fold.it was always more geared towards being edutainment than actually contributing solutions. Of the ~20 publications made related to fold.it over a decade, ~5 of them seem to have contributed to solving structures, while the rest of them are about the game itself.