EGLFS: QML superscrits not working (but working on X11)

[bitbang]

The following code is meant to show the formula e=mc squared, with a bold "e" and "2" as exponent:

Text {
            textFormat: Text.RichText
            text: "<b>e</b>=mc<sup>2</sup>"
}

When run on PC virtual machine (Debian 10, Qt 5.11, X11) it works as expected.
When run on embedded ( Debian 10, Qt 5.11, EGLFS) the "e" is in bold as expected, but the "2" is normal text size and position, like the ^and tags were missing.

Any hint?