iOS update 12.3 is stuck at update requested and has been for hours on my 2018 iPad Pro.

Are you able to turn off automatic updates? If you can, turn that off in the settings, restart your iPad and then try again to manually update. If you can’t do that or it doesn’t work, force restart your iPad. And then try again. This is how you force restart.

On an iPad Pro 11-inch or iPad Pro 12.9-inch: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then press and hold the Power button until the device restarts.

Force restarting is like rebooting a computer. Sometimes that can help reset things.

Did you try another WiFi network? Can you use iTunes instead to try to update?

I suppose that you went through the suggestions in here?

Get help with over-the-air iOS updates - Apple Support

I would close force the settings app, restart the iPad and then try again. You have nothing to lose since nothing is going on anyway.

Slowly swipe up from the bottom of the screen and about halfway up, release your finger to reveal the app switcher and to see the suspended apps. Find the settings app, then swipe up on the preview window of the app to force close it.

Restart your iPad and then try again.

There is one more thing that I may suggest and that would be to reset all settings. If you know about this or tried it already, forgive me for for suggesting it again.

You don’t lose any data when you reset all settings, but you do have to re-enter all of the device settings again and that includes WiFi network passwords. It’s not all that bad, but it can take some time to set all of your preferences back to where they were.

Settings>General>Reset>Reset all settings. When you do that, the device will reboot on its own and all of the device settings return to out of the box condition. You will be starting all over again with regard to the settings app.

That’s great. I’m happy to hear that you finally got it worked out.