In earlier years, the energy efficient "Ultra Low Voltage" CPUs of the U series hardly offered any performance, but manufacturers still packed them into workstation laptops. Even though the modern U processors are still considerably slower than H CPUs, at this point their absolute performance is high enough for new models such as the ThinkPad P15s Gen 2 to be able to deliver sufficient power for CAD applications.
https://www.notebookcheck.net/Lenovo-ThinkPad-P15s-G2-Workstations-with-ULV-CPUs-are-getting-better-and-better.545955.0.html