I found this post, which describes the basic problem, but it is closed:
Reading it gave me a good idea though. Instead of double-clicking on the script icon in Unity, I brought up VS2019 and browsed to the Solution file and opened it. Now it is providing auto completion for the UnityEngine.UI elements of the code.
In the 2D lectures I can see he is simply double-clicking on the script icon and getting this to work, so it sounds like there is a configuration in either Unity or Visual Studio 2019 that needs to be set for this.
That did help. I had moved from a VM to being native on my system and had forgotten to set Visual Studio as the external editor.
However, I think that in addition to that there was a setting I enabled that is not shown in the video. In Unit Preferences for External Tools there is a checkbox now called “Generate all .csproj files”. When I clicked that, closed everything, and restarted it I now see completion of the Debug name when I type “deb.”. That never happened before and I know I had set VS as the external editor in my VM version, so I think this is important.
Note that I am using VS2019 and Unity 2019.3.9f1, so this appears to be a new setting. Maybe the video needs to be updated to show this, since he is using VS2017 and Unity 2018 in it.
