Scratch asks for a “Scratch Link” so as to connect to micro:bit, but this driver seems to be provided for Windows, Mac, Android and Chrome OS but not for Linux. Am I right ?
EDIT : i read there is an experimental linux versioon https://github.com/kawasaki/bluepy-scratch-link
As a workaround I imagine we can still scratch on Linux, then we have to upload the programm here and then open it on Android so as to run it. Is that possible ?

Yeah, unfortunately, Scratch Link isn't officially supported on Linux. Only on Windows, macOS, Android, and ChromeOS.

You could try the experimental version, but I don't think it would be that stable.

You could send the project to the Android app by going to “File > Save to your computer” on the computer, and then you could send the file by plugging the Android device into the computer and sending it over USB, and in the Android app, you could press “Import” and open the sb3 file. Then you should be able to open it, but that method might take way too long…