The Notifications section on Mastodon has two sections at the top, "Mentions" and "All":
- If you click on Mentions, it will only show you notifications for replies and posts where you are mentioned.
- If you click on All, it will show you notifications for everything including favourites, boosts, replies, mentions, edits etc.
(Several people asked why their notifications weren't showing boosts or favourites. It turned out they had accidentally clicked on "Mentions" without noticing it.)