I see it is possible to assign nested breakpoints (f.e. for sin(x) I can assign a breakpoint to the whole function and/or to x; for sin(cos(x)) we can assign up to 3 breakpoints - and so on)
If this is intended, I propose to add something to identify when there is a nested breakpoint - f.e. a white border.
If this is not intended, "toggle breakpoint" should look at the surrounding math (if it is inside an existing breakpoint -> disable it, otherwise set a breakpoint).