Custom button issue: Tamron 28-75mm f/2,8 di iii vxd g2 / Sony A7 III

Just got the Tamron 28-75mm f/2,8 di iii vxd g2 and tried to set up the custom button on the lens for focusing.

Already installed the Tamron App and updated the lens to Ver. 2 (latest version).

If I set the lens button to be customized with my Sony Camera, the option in my Camera to set up this button is greyed out and says, that the lens is not compatible.

All other functions from the Tamron App are working with this button, except this one.

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Got any suggestions?