We didn’t add those options as usually H3-H5 are smaller font so the size can be the same on desktop and mobile.
We always try to limit the number of options and only add the most useful ones to keep the theme and premium plugin lightweight and fast.
If you need the mobile specific options for those as well, add this CSS:
@media (max-width: 768px) {
h3 {
font-size: 15px;
}
h4 {
font-size: 15px;
}
h5 {
font-size: 15px;
}
}
Adding CSS: https://docs.generatepress.com/article/adding-css/
Let me know if this helps π