I can use
sudo vncserver-x11-serviced & to start a VNC Server as a daemon.
I need to execute this command whenever I boot or reboot Raspberry Pi.
From https://www.realvnc.com/en/connect/docs/man/vncserver-x11-serviced.html, I learned that
sudo update-rc.d vncserver-x11-serviced defaults is the command.
vncserver-x11-serviced is in
/usr/bin, so I made a symbolic link in
sudo ln -s /usr/bin/vncserver-x11-serviced /init.d/vncserver-x11-serviced
Then, I executed
sudo update-rc.d vncserver-x11-serviced defaults as is written in the webpage.
However, when I try to access the Raspberry Pi RealVNC server using RealVNC Viewer, I have the error message.
What might be wrong?