Part of the reason Trump got steamrolled into a cognitive test was that in addition to his DOJ and some Democrats that Republican elites, even among his own cabinet, insisted he do so after aids would have to repeat their oral reports, which they had to do often. There was discussion among the cabinet in 2018 about invoking the 25th Amendment. The cognitive test was conducted to shut those discussions down.
Not to mention the media had a field day with the results. Trump claiming it was an intelligence test, the scrutiny of the ease of the test containing words with which Trump likely hears every day…Person, Woman, Man, TV… this seemed to be enough to shut down cabinet conversations of the 25th amendment, but now the media had the people alarmed that such a test was even necessary.
The difference is that no one in Biden’s cabinet have considered invoking the 25th amendment, at least out loud, as there is currently more unity within the Democratic Party now then there was in the Republican Party in 2018. After the 2020 election finally exposed the Republican infighting which is why Republicans right now can’t seem to organize anything other than accepting that Trump is the only thing their constituency is sure about; even with what little Trump’s endorsements contributes to other politicians to get them elected. Yes, the people like Trump but his endorsement is not a guarantee unless it’s a primary of some kind.
Meanwhile, there have been no reports of Biden’s aids having to give oral reports, no level of dissension among Biden’s administration, at least not at the level of Trump’s, and the only one calling for such tests are mostly rightwing media.
And, even if Biden did take a cognitive test, the result would likely be the same as Trump’s. The public asking why it was even necessary and the media scrutinizing the ease of the test.
In short, yes, Biden has nothing to gain.
But aside from a few gaffes, which if one bothered to compare, is still no where near the number of gaffes by Trump or any other elderly politician.
I personally sympathize with people who say we should elect fewer elder politicians to office. But since our choices are both suffering from symptoms of dementia; it’s rather a moot point.
A dementia-addled President is in the cards no matter if you pick choice A. B. Or even C. (Because C. will never get enough electoral votes.)