Hi,
Please try this:
$ sudo apt-get install libprotobuf-dev protobuf-compiler
$ pip3 install setuptools==49.6.0
$ pip3 install cython==0.29.36
$ wget https://github.com/protocolbuffers/protobuf/releases/download/v3.5.1/protobuf-all-3.5.1.tar.gz
$ tar -xvzf protobuf-all-3.5.1.tar.gz
$ cd protobuf-3.5.1/
$ ./autogen.sh
$ ./configure
$ make
$ sudo make install
$ pip3 install onnx==1.12
Thanks.