In poking around trying to make sense of this new 20.04 LTS installation, I can't seem to bring up the Activities screen. The doc says to press the Super key. OK - I'm using a standard Windows keyboard - WHAT is the Super key? I was pressing the key with the Window on it, but that just brings up a search menu. Ctrl and Alt by themselves don't work, and the hot-corners don't work either, AND I can't find out from Settings whether they are even defined.
One thing may be causing a problem. I'm using an LG TV as a monitor connected to a Dell 790 via an HDMI cable. It sees like the Ubuntu driver is making the screen image a little too large for the surface area of the TV screen, because the dock at the bottom is cut off (it's visible, but only the top 2/3 of the icons show) and the top bar with the date on it doesn't display at all. I only discovered it was there when I set the display scale to 200%. This is not a problem I had with this TV when it was connected to a Mac Mini.