first download unity hub then from there unity
link: https://public-cdn.cloud.unity3d.com/hub/prod/UnityHub.AppImage?_ga=2.47295271.1647170687.1641982584-645973930.1641982584
download Linux dowload assestent
cd ~/Dowloads
chmod +x UnitySetup-2018.2.7f1(here you have to put your version)
cd
~/Downloads/UnitySetup-2018.2.7f1(run the installer)
and to lanch unity, just type,
~/Dowloads/UnityS-2018.2.7f1(again you have to put your vertion here 2018.2.7f1)