After few hours working to solve this, I understand what was wrong and how to solve it.

In the file explorer, I went into C:/Android/android-sdk/. In this folder, there is some folder but I looked at build-tools/ and platforms.

In build-tools and I have the folder 28.0.3 which corresponds at Android BuildTools 28.0.3 so this one is good.

Then, in platforms folder, I only have android-28 folder which means Android Studio didn't installed Android 29 correctly (I tried with android 26, 27 and 30 but none of these were installed correctly or in another folder). There is my main problem.

So I asked one of my friend to send me his android-29 archive to unzip it into my platforms folder and then no more errors and I can use Flutter without trouble.