When confronted with the getting started screen in Dynamo 2.12, the user is led to believe that to use this new node autocomplete feature, they have to Alt + left click on the input or output.
After some time trying to make it work and fruitless online searches for other people who might have had the issue of it not working, I found the solution when I went to the help button next to the setting that turns on this feature.
So, apparently one has to double click instead of Alt + click.
Also, NodeAutocomplete is not enabled by default as the first description claims. It is an experimental feature that is disabled by default.
Hope this helps other people caught in the same issue.
It’s certainly a nice feature, but it’s just sad to think that a exciting new feature isn’t working for you