This was driving me crazy as well but got it fixed!  I have a MacBook Air with just the trackpad so no settings adjustment was working for me.  Had to install SF Pro font on my Mac and then install them to Figma.  Follow the steps in this article: https://help.figma.com/hc/en-us/articles/24037833895831-Get-started-with-Apple-s-UI-kit

I solved the issue for me...I’m not sure if this is what anyone else was experiencing.  So double click the text you want to edit and go under “Typography” in the Design Panel.  To the right of the pre-selected style, a little symbol only appears if you hover over the area and it says “Detach Style”.  The symbol looks like a chain that’s breaking.  Below that is another that says “Detach Variable” next to the pre-selected variable.  Now I just created a new page and didn’t create any style or variables so I’m not sure how these got created?  It’s taken me hours to figure this out which feels so silly.  Can’t even change the font in a program.