When I inserted a character of

https://de.wikipedia.org/wiki/Unicodeblock_Notenschriftzeichen

e.g. 𝄾

into the text of a song for marking an eighth rest for a stanza which has no
text for a note.

Lilypond puts this character correctly into the PDF but the frescobaldi editor
show only two squares and not the character

Hi Peter,

I'm unable to reproduce this with frescobaldi version 3.0.0+ds1-1. Could you
please let me know if you still experience this bug with the latest version of
frescobaldi?

Best wishes,
Ryan

This is almost certainly an issue with the font in the text pane not having
a glyph for that unicode point.

if your system text font doesn't have the glyph you'll get two squares

Regards
Grant.