AppStream metadata for the tomboy-ng package are not generated:

https://appstream.debian.org/sid/main/metainfo/tomboy-ng.html
https://appstream.debian.org/sid/main/issues/tomboy-ng.html

Because of this, tomboy-ng is missing in modern package management UIs such
as GNOME Software or KDE Discover.

This seems to be caused by the AppStream metainfo file being duplicated in
the package:

/usr/share/metainfo/io.github.tomboy_notes.tomboy_ng_notes.appdata.xml
/usr/share/metainfo/io.github.tomboy_notes.tomboy_ng_notes.metainfo.xml

Please remove one of these files and keep only the other one.

Sorry, this message was only just found in an (unexpected) Spam Folder.

Thank You I have been unable to determine what was wrong with the
Metadata and, eventually, gave up.

I will try to address this issue with next release.

Davo