Musescore 4.5.2 : Cannot play a part that I created

Hello,
I am trying to create a music sheet from scratch, but I am not able to get sound on what I wrote.
I would like to be able to hear both my notes and my chords, but I am unable to hear either.
I think my sound system is properly set-up, because when I open another music sheet, downloaded from here, is makes sound just fine.
Why am not able to get sound from my own sheet music ?

I wrote the notes on the staff with a midi keyboard,
and I created the chord symbols by selecting a note and then shortcut "Ctrl + K" and writing "C", "F", etc.

To illustrate my problem more clearly, I am uploading :
- a screenshot of the playback options that I have on my sheet (as you can see : not able to unmute my staff and the chords eventhough they are selected in the sheet)
- the .mscz file of my sheet music that doesn't have sound : Essai_Composition_01
- the .mscz file of the sheet music that I downloaded from muscore and that does have sound : Passacaglia-Handel--src

Thank you for your help, and have a nice day