I want to use this topic to collect some insights into UX best practices around notifications. Not all are on top of my head, so I will add replies when I remember the sources.
@aschrijver mentioned the other day, that
Matrix is a context-switching training apparatus.
That got me thinking. I know, that notifications can be bad, i.e. cause stress:
I originally answered, that by design (even though perhaps not intended), a lack of customisation for colour, typography or layout makes it harder to recall, where something was mentioned. You perhaps remember from school day, that a certain fact was written on the right page of a book in the lower third part. But on apps everything looks the same. A good UX would allow some level of customisation. For example, Threema allows to define a background image to chat rooms.
@Gusted pointed to keyboard shortcuts on Discord, that allows to traverse easily between mentions. That allows for a quick catchup (with context) but requires recalling a hidden feature: the keyboard shortcut itself.