Cannot keep MacBook Pro from automatically restarting after installing new system software

I'm selling my MacBook Pro and I followed Apple's instructions (https://support.apple.com/en-us/HT201065) on what to do to prepare the computer for sale. The official instructions say to allow it to re-boot, which will then bring up the set up screen for the newly installed Catalina. Then press command-q and the computer will shut down and stay shut down until the new owner pushes the start button. At that time she/he will see the set up screen and then they can take it from there, like a factory fresh Mac.

The problem is that pressing command-q does nothing, leaving the set up screen continually asking for your wireless network. Another post (https://discussions.apple.com/thread/6351507) said "Turn off the machine. Hold down the power button until the machine turns off, then immediately hold down 'command q', choose 'shut down' from the apple menu; whetever you have to do to shut down the computer so the new owner can press the power button and set up the machine like it was "factory new".

This does not work on a MacBook Pro running Catalina. Holding the power button down does shut the computer down but does not bring up any type of apple menu and therefore no 'shut down' option. Instead the computer restarts and shows a rotating globe, beneath which is a menu to choose your network.

My MacBook Pro did this all night despite the case being closed. When I picked it up this morning, it was very hot and stayed that way as it endlessly displayed the spinning globe and network menu.

Lots of used Macs are on the market, so many people must know how to keep the set up menu from automatically re-appearing, ad infinitum.

I've been using Apple computers for 40 years, but this is a problem I have never encountered before. I’d love to learn how to keep the Mac shut down until the new owner boots it up. Thanks in advance.