MuseScore is a free and open source music notation application.
Is MuseScore 4 a Sibelius killer?
Installing MuseScore on Linux
MuseScore 3 is available through standard software channels such as apt in Debian. MuseScore 4 (a substantial upgrade) is distributed as an appimage (as of March 2023, and may be available in Debian Sid). Not a great option, but not as bad as flatpack. Instructions as follows for Linux and the Linux subsystem on Chromebook (view a new video on this subject). At some point MuseScore 4 will be available through standard repositories.