When a user with a Runner license tries to Debug a script the option is disabled.
Foundation/User Governance - all versions.
In order to use debug, the user will need to be granted the developer role. The developer role does not give the user access to create scripts (only a Studio license will do this), however it will allow the runner user to debug. We require runner users have this role to debug, as they could make data changes during the debug process.
Assign the user the developer role from Foundation.