Hi Ignacio, it is better to send a minimal working example (MWE) instead of screenshots. Here is one. This should work:
\version "2.20.0"
\markup {
\override #'(font-name . "Ubuntu Thin") "Test"
}
As you are using Frescobaldi (I hope a recent version), you can search
for the fonts this way:
Tools > Document fonts
The name there should be exactly what you can use in the code above.
If that is not the case at your end, please report back with exactly the
code you use.
Cheers,
Joram
