In my case I’m using Manrope, the latest version, replacing the one in the system font folder.
I know there is another related issue (currently closed) referring to that is a font problem, due the lack of stroke weight definition of this decorator in the font itself.
Even being that truth, it doesn’t change the fact that underline is showing when a letter has descent and it only happens with rendering while presenting, so it must be related to the renderer, which probably is copying the smaller surface rectangle as possible, causing the decorator disappear unless there is something drawn below the baseline, like the descent in a “p” for example.
Please take a look at this, because even if it could be solved by new versions of the font, the truth is that Figma comes with a bunch of fonts ready to be use and they should guarantee that are able to show a underline style. It is such a common thing in any design system or prototype, just think on a link.
Thanks in advance and regards.