Unfortunately not, as Bluesky is structured you cannot remove a follower. Only the one who follows someone has the "power" to remove that follow. By the way I did a quick check on your followers with my app, 403/708 have posted after August 1st. You are right on the inactivity you mentioned.
If you block them does it remove them as a follower? Could we implement a block inactive/likely bots account to achieve this as a workaround?
It doesn't remove them as followers, meaning that if you unblock them they will again be your followers, but, as long as they are blocked the behavior is the same. They won't be able to see your profile nor your posts. I've already implemented this solution in my app's advanced filters.