Why have so many questions about past polls, mainly for the 2016 and 2020 Presidential elections, started showing up at the head of the page? Surely they are either moot, or trivially answerable by a search of news articles?
They are showing up because someone has edited the question/answer or a new answer has been posted. Most of what you are seeing are old questions that are just reappearing on the front page.
As for your second question it doesn't matter if they are moot or trivially answerable as that is not a criteria for a valid question on this site. What matters is that they are good questions that can attract good answers. What you are asking is also missing a critical point in that what is trivial for one person to find might be hard/impossible for someone else due to a lack of knowledge on what to search for.