Hi @osmanpasha, welcome to the forum 
I remember there being an issue with our build process for Ubuntu 20.04 a little while back, but unfortunately don’t think it finished getting fixed. From memory it’s an issue with the installing prerequisites step - the script in ArduSub-stable is outdated for Ubuntu Focal. We were discussing updating it to the one currently in the master branch, but @williangalvani pointed out that the latest commit for that file would likely cause issues with our existing system. It may work if you install using the master script, but you likely need to roll back to before that commit.
I’ve brought this up with the software team so we can figure out what needs to be updated/changed, but I’m not sure how soon we’ll be able to get the script updated correctly. If you decide to try it then please let us know how it goes
Perhaps also worth noting this post, where the user apparently got around the issue by building with the Eclipse IDE.