AutoHotkey Community

Is there any built-in key for it or should I try to create/search for one?

Yes there is: Ctrl-q is a toggle for commenting / uncommenting a block of selected text. And Ctrl-Shift-b comments a block of text as a box (rather than commenting out each line); it is not a toggle.
Both are on the "Edit" tab.

@frabjous
How to do it "toggling"? It's kind of uncomfortable without it.