After thorough discussion with Matlab support and several relevant forums (Ubuntu, NVIDIA, ...) the final result is as follows:
- Installation of NVIDIA CUDA Toolkit 10.x (only supported by recent version of MATLAB) on Ubuntu 20.04.x is very problematic or totally impossible task (depends on your Linux skills). Better forget it ... !!!
- The only possible way how to reliable install NVIDIA CUDA Toolkit 10.x together with recent Matlab on Ubuntu OS is downgrade to the Ubuntu 18.04 version
- Forthcoming Matlab version R2021a will be support NVIDIA CUDA Toolkit 11.0 (compatible with Ubuntu 20.04) which is probably good news, but so far not possible to verify it
So finally, if you're working on Ubuntu 20.04 LTS and want to use CUDA kernel objects or a GPU coder, you're out of the game.