Blender 2.91-

Where is the Cap Fill Ngon located in this new software 2.91? I am trying to do a tutorial making a robot dog, but they are using an older version.

You have to open Adjust Last Operation panel, at the bottom left corner of 3D View.
Or press F9.
It should be called Fill Type, Cap Fill Type or Base Fill Type.

Thanks for trying to help me. I am using version 2.9 and was trying to follow a tutorial for beginners. I just started using blender, so I am clueless. I found 3D view port F5, but did not see the adjust last operation panel. The F9 toggle - I get pop up saying edit mode. Not sure what I am doing wrong.

F5 is a free keymap.
Shift F5 is the shortcut to change an editor into 3D Viewport.

By default, there is a 3D Viewport visible in Layout or Modeling Workspace.
So, there is no need to press F5 or shift F5.

But in left bottom corner of that viewport , you should see a line indicating last action done.
That panel is closed by default.
You just have to click on it to open it or press F9 to see an equivalent floating panel under mouse.

If it says Toggle Edit Mode ; that means that last thing you did was to switch active object to Edit Mode.

So, you will not see options relative to a Cylinder or Cone creation.

But if you press F9, just after adding a Cylinder or Cone, there will be a Fill Type setting among other settings relative to Cylinder or Cone creation.

It worked.
Thank you so much for your time. I really appreciate it.