Another thread on this as well.
https://boards.straightdope.com/t/no-mouseover/912436/31
Only works fully in the SDMB themes, and does not work if you have a touch screen. Confirmed this by disabling touch.
Found a discussion on dicourse development.
https://meta.discourse.org/t/user-experience-on-discourse-with-optional-touch-input/40190/12
looks like there was an option sometime in the past, but it got removed, and still looking for a working automatic way to get this right.