entering tam-tam via “add solo player” suggests gong and creates a-line staff.
Gong is a pitched percussion, but tam-tam is an unpitched percussion.
Please refer to: https://www.vsl.co.at/en/Instrumentology/Percussions
For clarity, this looks like a mis-translation in the Italian set of instrument names.
To reproduce,
Set Engraving Options > Language > instrument names to Italian.
Add a new instrument to an existing player, or add a new player.
Type tamt into the instrument search and see that the filter selects “Gong” from the list.
prko, for your own purposes you can fix this yourself:
Create a “gong” instrument. From the > menu, click Edit Names.
Type Tamtam into the appropriate text boxes.
Tick the “Save as Default for instrument” tickbox.
Hit OK.