You want to use chattr +i (make the empty file immutable)

I'm on my phone now so I can't check if something has changed, but what you want to protect from change is the directory, not the files. A file can be deleted and created again if the process can write the directory.

yeah, should work. Will try readonly on windows too.

Now I can't see it anymore, but shouldn't the model be under chrome://on-device-internals/ -> model-status?

Maybe you can uninstall there too.