com.microsoft::FusedMatMul operator not implemented?

[MG-EuS]

I have an onnx model that was exported form pytorch with opset_version=14. Now I try to convert it to tensorflow using onnx-tf like this

import onnx
from onnx_tf.backend import prepare

onnx_model = onnx.load("my_model.onnx")
tf_rep = prepare(onnx_model)
tf_rep.export_graph('./tf_export/my_model')

but it produces the error message

...
raise BackendIsNotSupposedToImplementIt("{} is not implemented.".format(

    BackendIsNotSupposedToImplementIt: FusedMatMul is not implemented.

So it tells me that the operation com.microsoft::FusedMatMul is not supported by onnx-tf, right?
What can I do from here? Do I have to implement it myself? How would I do that? I have searched for documentation in onnx-tf but not found much. Maybe someone had similar problems :)