Nope nothing missing, help is now search only.
It's actually worse than you think though, do a search for line and you will see that the results for drawing a line are in the middle of the results.
Ok, let's say that I don't know about convertpstyles, but I do know that I can change a drawing from style based plotting to color based plotting, let's try some obvious choices:
change drawing from style based plotting to color based plotting
change drawing from using stb to ctb
change drawing to color based plotting
Hmm...nothing useful with any of the obvious....so I use Google by proceeding the first search term with AutoCAD, I instantly find out that the command name that I need is convertpstyles, but I don't want to read the whole article, so let's go back to AutoCAD help and search for convertpstyles.
The help article does not show the steps, nor any screen shots of the process.
Also, remember that offline help files are not installed by default, if you want to use offline help, you have to download it separately from AutoCAD and install it on each system manually, there isn't even a way to roll it into a deployment that I have found yet.