"I had heard that tunnels were a good first step for rolling out super conducting cables, but that doesn’t seem to be a thing."

Yeah tunnels underground would be better for superconducting cables, but it is indeed not really a thing as the cooling and installing and maintainance would be waaaay more expensive, than just using higher voltage. Or if one really cares about the loss, use direct current - but we are talking aber very small distances here.

If superconducting would be easy, we likely just would have fusion plants everywhere with no need for transporting electricity long distances.