Hi Christian,
I'm Adzim. Thanks for using Intel Community.
I have reviewed you error logs and look like this is a known issue.
I have saw that you already tried to fix the issue by installing the WSL on your OS.
I believe that you already refer to this:
https://www.intel.com/content/www/us/en/programmable/support/support-resources/knowledge-base/tools/2019/how-do-i-install-the-windows--subsystem-for-linux---wsl--on-wind.html?wapkw=WSL
But the difference is that they have used the Ubuntu version 18.04 while you are using version 20.04.
I'm wondering is this can make a difference in solving your issue.
Would you able to use Ubuntu version 18.04 LST instead of 20.04?
After the installation has completed, can you launch the Nios2 Command Shell?
Thanks,
Adzim