Reduce margins (gradually ?) when the viewport is small.
It is possible to change the margin size in the layout parameters, but it should be overridden when window size is too small
I often split my screen on my laptop between two windows : AnyType and something else (a web page, an online meeting). Screen real-estate is pretty important at this point.
Maybe gray out the “Set layout width” in the layout parameter when width is small and explain this to the user.
I collapse the sidebar manually but another enhancement could be for it to unpin when window size is too small.