Save and Load drumset in Linux

I'm using MuseScore 3.6 in Ubuntu Studio 20.04
When saving an edited drumset, the file is saved without an extension (is this a correct behavior?)
When trying to load the drumset, the dialog cannot find the file (the file exists if I check it with a file browser)

I believe this is just an extension issue, unfortunately I don't know the correct extension for a drumset. So if anyone is kind enough to tell me the extension, I will be very grateful =)

It is a rather common problem with Qt applications.