I just installed RetroPi in Raspbian and now the install manual for RetroPi (https://retropie.org.uk/docs/Manual-Installation/) says I need to log out of PIXEL to use RetroPi. How can I do this? I have searched google and can't find anything that says how. Thanks in advance!
Of course, if you have the money, buy a dedicated RetroPi SD (32GB ~$10).
Set Raspbian to boot CLI (command Line Interface); top-left pi icon->Preferences->"Raspberry Pi Configuration" -> "System" Tab->Boot: "To CLI".
and when you want to run PIXEL Desktop again use the startx command. "Shutdown..." menu will change to "Exit to command line"