Font size grayed out in typography block

When I try to change the font size of a paragraph or other block, using the dropdown under “typography” in the gutenberg block sidebar, the dropdowns that say “default, normal, medium, etc” are greyed out and I can’t change font size. I thought it might be because of the theme I was using but this is happening on all five of my sites and they all use different themes. I think this happened after the last WP update. I have searched everywhere to see if there was a setting I need to change but I can’t find it.