Thanks Bhack.
The virtual environment doesn’t help. However, I reinstalled tensorflow with different version 2.5.0  (instead of 2.6.0) and with Nvidia TensorFlow container 21.07 and it works great!
Instead of using (doesn’t work for me, by default installing tf 2.6.0 version and no container):
“sudo pip3 install --pre --extra-index-url https://developer.download.nvidia.com/compute/redist/jp/v46 24 tensorflow”
I used (runs excellent):
“sudo pip3 install --extra-index-url https://developer.download.nvidia.com/compute/redist/jp/v46 24 tensorflow==2.5.0+nv21.07”
Thanks a lot for you help!