Mixamo auto control rig won’t attach

Maybe try exporting the Mixamo rig in a different FBX format (Binary or ASCII) or try using the original pose (FBX) instead of the default T-pose. After that, make sure to ONLY import the Mixao Auto-Rigger script in your maya script documents (C:\Users\Name\Documents\maya\scripts) and NOT the version script (C:\Users\Name\Documents\maya\2020\scripts).

You can also check out Academic Phoenix Plus' video on how to set up the script properly: https://www.youtube.com/watch?v=YnNt9qA1Xf4&ab_channel=AcademicPhoenixPlus 

Hope this helps

the reason Adobe dropped the autorig script is because it doesn't work well & Mixamo has changed their rigging system after dropping it so the odds are against you mate

as this is really a Maya question your best bet would be to ask on their forum to see if anyone still uses the script

https://forums.autodesk.com/t5/maya-animation-and-rigging/maya-control-rig-script-for-characters-rigged-with-mixamo-s-auto/td-p/5514918