The process of adding the initial formatting (highlight, bold, italic, italic+bold, strikethrough) to a text selection is relatively easy. However, it is not very easy to make adjustments.
Once the cursor is within a formatting range (for example a highlight), the
== characters at the bounds of the range become visible in live preview. In this state, it would be useful to be able to press a hotkey (for desktop) or do a triple tap/click within range (for desktop/mobile) in order to select the text within the most immediate formatting range. Once in this state of selection, it would be useful to be able to adjust the bounds of the formatting by interactively dragging handles at the edge of the formatting selection. I could go either way, but it might be useful for all of the note’s formatting handles to become active within this state.
Currently you can manually select the text range, toggle off the formatting, adjust the selection, then toggle the formatting back on.
Related request: [Feature] Easier highlighting, bolding, italicizing