Which iPad model? Which iPadOS version? Which monitor model?
In any case: according to their manuals most HP monitors with touch functionality (like e.g. the HP E24t G4 FHD) need a video-
AND USB-connection to enable/use it.
On Windows there is an automatic driver installation when connecting these monitors, IDK whether this is just for the video part (monitor profile etc.) or also required for the touch functionality.
Because you need a dongle/hub anyway to connect iPad and monitor, what happens when you additionally to video connect them with the USB-cable which came with the monitor (assuming you have access to a hub like e.g.
this)?