The Ryzen CPU and Renoir GPU are too new for all kernels supported by Ubuntu 18.04 (5.4 is the latest supported). The notebook will boot with 18.04.5, but a lot of things will not work (sleep, screen brightess, audio, graphics only works in a limited way etc.).
This tutorial shows the steps necessary to be done to successfully run the system with full support for the GPU and other peripherals.