Where am I going to import something that is not in the issacsim library, such as a fetch robot that is not in the library
You may want to start by searching the forum or the internet to see if any Fetch robot URDF files have been used by other users. If you find a suitable URDF file, you can import it into Isaac Sim.
@1291367587 you can use any of the URDF files available online, many robot manufacturers provide this