there is already a screenshot mechanism, with the insertion of a PNG image directly from the clipboard. It already works, without editing. Already half the work is done. But a naked picture is often useless.
Of course, for a programmer to set the task of "a graphic editor" is a difficult task.
For sure, there are open codes of simple editors. In fact, only 2 functions are needed: text and line (squares and circles are near). may be a choice of colors, or red (default). That's it, no more. A lot of work.
Of course, there are a million external apps, no need to offer ShareX. Everyone can handle it on their own, if it's slow and hard. Text and lines are needed in Vivaldi.