I experience anemoia quite a lot. It is typically triggered by several things, like discontent with current situations and wondering about paths not taken. I experience it often when I view YouTube music videos from the 'classic rock' era of the 1970s-90s, and in some history subreddits on Reddit (typically those where members upload photos of their families in past decades or of cityscapes from times long gone,) or watching old movies and TV shows from my DVD library.
Regarding YouTube, I saw a comment that had 1000's of likes where the poster said that YT is the closest thing we have to a time machine.
Anemoia is very melancholic.
All that is gold does not glitter,
Not all those who wander are lost;
-J. R. R. Tolkien