I've just installed Unity 2019.4.20f1 and Rider 2020.3.2, and created a new unity project.

I set the external editor to the rider executable (in /usr/bin/rider in my case) I opened the sln in rider and it installed the rider plugin.

Now with both open (and having tried opening both with the other), rider refuses to connect to unity (shown by the icon down the bottom).

It should show connected but hovering just shows the error in the title. Play button in Rider is greyed out.

I've checked the first page of google and nothing there seems to fix the issue.

Steps to reproduce:

• From the AUR, download unity-hub and rider
• Install the latest recommended Unity version from hub
• Create a project in unity hub and open
• Set the external editor in unity prefs to /usr/bin/rider
• Create and double click a script

Update: Just tried Unity 2020.2.5f1 with the same issue