how to do a hard shutdown on my iphone 10

Try a forced reboot. Its hardware based, so whatever is on the screen should not matter:

On an iPhone X, iPhone 8, or iPhone 8 Plus: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then, press and hold the Side button until you see the Apple logo.

This will force reboot the iPhone

Jake...

Restart your iPhone X.

Instructions > Restart your iPhone, iPad, or iPod touch - Apple Support

I don't know how you've been trying to turn your iPH X off, but you could try this often overlooked way of doing it without pressing any side buttons: go to Settings > General, and scroll right down to the bottom, where you'll see an option to turn off your phone. Tap on it, and you'll get the screen with the "Slide to Off" option. Hope this helps you! Regards, Ian.