QEMU itself does NOT provide any RDP. QEMU supports following "display" outputs.
qemu-system-x86_64 --help 2>&1 | grep -- '^-display' | sed 's/^/ /'
-display spice-app[,gl=on|off]
-display gtk[,grab_on_hover=on|off][,gl=on|off]|
-display vnc=<display>[,<optargs>]
-display curses[,charset=<encoding>]
-display egl-headless[,rendernode=<file>]
-display none
For some output modes monitor console is multiplexed, ie. it could be accessed from the output mode, eg. one could access monitor console while having QEMU app running with GTK display mode.
But... QEMU monitor could be accessed while using RDP, monitor console could be linked to various I/O "devices", it could be accesses via UNIX socket, TCP socket etc... One should understand that access to monitor means access to virtualization host, one could open/save files via monitor. Probably preferred access method if monitor is not multiplexed is via TCP socket with TLS client authentication or via SASL.
telnet
if you want...-vga virtio
is alias for configuring emulated (or paravirtualized) VGA card, it has nothing to do how QEMU launches the output, you are confusing-vga virtio
with-diplay <mode>
option. Anyway, RDP is just inside our Windows VM, QEMU monitor is a kind of management console for QEMU process. See qemu.readthedocs.io/en/latest/system/invocation.html#hxtool-3 and qemu.readthedocs.io/en/latest/system/invocation.html#hxtool-6