Visit https://gns3.com/software/download
Run these commands:
What we are doing is adding the repo/ppa for gns3, then updating apt and then install gns3 and the gui.
sudo add-apt-repository ppa:gns3/ppa
sudo apt update
sudo apt install gns3-gui gns3-server
Run gns3 from the terminal by typing "gns3"
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