I just have upgraded from Ubuntu 19.10 to 20.04 and everything works so far. Only problem that I have now is, when my laptop (Lenovo P50 with Quadro M1000M) is connected to an external monitor in mirror mode through a USB C (Laptop) to DisplayPort (Monitor) adapter and I close the laptop lid that the system is lagging so much that is unworkable. As soon as I open the lid again, everything works fine immediately. I am using the X.Org X server option as I did before upgrade where it worked fine. I have tried the Nvidia driver options 440, 435, and 390 but it doesn't recognize external monitor at all. I also have tried it through the HDMI to HDMI connection, but same result. Closed lid causes the problem. This a major issue as I use the external monitor most of the time and this forces me to have the monitor always open.
Does anyone has some ideas how to fix this?