Is there a way to enforce straight mouse movement(horizontal, vertical, diagonal) in macos?
You can, in fact, make specific dedicated underlines.
In the top bar, the pencil tool, there are options for Underline &amp; strikethrough.
Both will track any text you select, letter, word or paragraph…

Giving this [the blue highlight is the selection, the red line is the added underline]



Instructions from my beer-making xmas prezzie ;)