Can R8000P be used as an AP or an extender?

> [...] I would like to use it as a wireless AP that I could wire my
> desktop in to. [...]

   Using the standard definition of "wireless AP", I believe that that
makes no sense.  Start again.

   What exactly, do you want to connect to what, exactly, how, exactly?

   A wireless access point (WAP) uses a wired connection to the
main-router LAN.  (A client device can connect to the WAP with a wire or
a radio.)  If you want a wireless connection between the main router
("Orbi and a satellite") and the R8000P, then you don't want to
configure the R8000P as a WAP.

   If what you want is a wired connection between your "my desktop" and
the R8000P, and a wireless connection between the R8000P and the main
router, then what you want is to configure the R8000P as a wireless
bridge.

   In that case, you might be doomed; I see nothing about a wireless
bridge mode in the R8000P User Manual.  (But see below.)

   Visit http://netgear.com/support , put in your model number, and look
for Documentation.  Get the User Manual (at least).  Read.  Look for
"bridge", but don't expect to find anything relevant.  For comparison,
you might fetch the User Manual for an R7000, and look for "Set Up the
Router in Bridge Mode".

> I don't have Step 6 the way it's explained.

   If you _did_ want to configure the R8000P as a WAP, then you might
look in the R8000P User Manual for "Use the Router as a WiFi Access
Point".  You'd want the "Router / AP / Bridge Mode" control, not
"Wireless Settings" on that ADVANCED > Advanced Settings page.

   Interestingly, although I found nothing relevant in the R8000P User
Manual, that "Bridge Mode" option does look encouraging, and might be
worth a look.

> Once I set it to AP Mode and remove the wired connection to the Orbi,
> [...]

   ... you'd absolutely be doomed.