Hi pearswnt,
First, we'd recommend restarting first, which can help. Next, make sure you have the latest iPadOS installed.
Restart your iPad - Apple Support
Update iPadOS - Apple Support
Then, if the issue continues, this page not only has info for connecting your iPad to a display, but also what to do if it's not showing up as what you described as happening.
Connect iPad to a display with a cable - Apple Support
Connect your iPad if it has a USB-C or Thunderbolt / USB 4 connector
On a model with a USB-C or a Thunderbolt / USB 4 connector, you may be able to connect iPad to a USB or Thunderbolt 3 port on the display.
If the charge cable that came with your iPad isn’t compatible with the port on your display, TV, or projector, do the following:
1. Plug a USB-C Display AV Adapter or USB-C VGA Multi-port Adapter into the charging port on iPad.
2. Connect an HDMI or VGA cable to the adapter.
3. Connect the other end of the HDMI or VGA cable to the display, TV, or projector.
4. If necessary, switch to the correct video source on the display, TV, or projector. If you need help, use the display’s manual.
5. If the display doesn’t turn on when you connect it to iPad, unplug it from iPad, then plug it back in. If that doesn’t work, unplug the display from its power source, then plug it in again.
See the Apple Support article Charge and connect with the USB-C port on iPad Pro.
If the issue persists, let's get in touch with Apple Support for some additional options. Get Support
Cheers.