When the sidebar width became adjustable it was a welcome feature.
The notification boxes were wider than the sidebar and if you were ticking off tasks then then the tickboxes could easily get hidden behind the notifications make you have to either wait or manually close the notification.
But now it has a new usability issue; accidentally grabbing the grabber when you’re trying to tick a task and throwing the sidebar width across the screen.
Locking the sidebar should be an option.