Is there a way to control the webOS OSE screen on other devices such as PC and ipad using vnc?
VNC is not tested on webOS OSE.
(It is totally unknown whether it is possible or not.)
I also don't know the vnc is available or not on webOS? But, I guess, if there is any wayland-supported VNC server, maybe you can connect from your a VNC client to a VNC server that runs on the webOS.