But after modifying the file, I launched Lightroomt again, it behaved as if it was the first launch and I had again the tutorials and ... the "Use Graphic Processor" option checked again.
This could mean that you made an error when editing the prefs file, like forgetting the comma after false, or accidentally saved the file with a different name. In both cases LR would probably recreate the preferences file, and useAutobahn would be set to true by default.
Also make sure that LR is not running while editing the preferences.
Adding to what Per said, when you edit the file, make sure it is a text editor (like Notepad on Windows) that preserves the character encoding and doesn’t add any extra formatting like WordPad or Word might do.
Using Notepad, I have three options for character encoding: ANSI, Unicode and UTF-8. The file needs to be saved as ANSI encoding, otherwise LR gets an error and will recreate a new one with the default settings include UseAutoBahn=true.
Thanks a lot. It worked !
Lightroom is no longer using the GPU, and I don't have these freezes anymore.