I encountered this problem a few weeks ago with version 1.21.6, and I finally figured out how to fix it without losing all my worlds. I pressed the Windows + R keys and typed '%appdata%.' Then, I clicked on 'Roaming,' then '.minecraft,' and then I simply deleted the 'launcher_profiles.json' folder. After that, I reopened the launcher and the error was fixed. Hope that helps! :) 🙂
nina corrêa
I encountered this problem a few weeks ago with version 1.21.6, and I finally figured out how to fix it without losing all my worlds. I pressed the Windows + R keys and typed '%appdata%.' Then, I clicked on 'Roaming,' then '.minecraft,' and then I simply deleted the 'launcher_profiles.json' folder. After that, I reopened the launcher and the error was fixed. Hope that helps! :) 🙂