ActivityPub posts can be very long. If I come across a very long post that I don't want to read, I have to start quickly scrolling through it which can take a long time. Then I overshoot the end of the post and tons of short posts start rushing past due to the momentum of my scroll. So I have to backtrack to the end of the long post. This is not a good experience and it could be avoided by collapsing posts longer than a certain length. At least having an option in settings would be good, but I feel like most people would expect this to be the default since most Mastodon posts are relatively short.
Moshidon implements this very nicely.

ActivityPub posts can be very long. If I come across a very long post that I don't want to read, I have to start quickly scrolling through it which can take a long time. Then I overshoot the end of the post and tons of short posts start rushing past due to the momentum of my scroll. So I have to backtrack to the end of the long post. This is not a good experience and it could be avoided by collapsing posts longer than a certain length. At least having an option in settings would be good, but I feel like most people would expect this to be the default since most Mastodon posts are relatively short.
Moshidon implements this very nicely.