Hi jthunes,
Welcome to Apple Support Communities. We understand that you're having an issue with using Notes in Dark Mode. We'd like to help.
When your iPhone switches to Dark Mode, have you tried to manually move the note even though you can't see the scroll bar? If you place your finger on the right side of your display, does it still move when you drag your finder up and down? We ask because this is a feature that should be available in both modes.
If you tried that and it's still not working, closing the app, restarting the iPhone, and trying again can help.
How to close an app:
iPhone X and later
- From the Home Screen, swipe up from the bottom of the screen and pause in the middle of the screen.
- Swipe right or left to find the app that you want to close.
- Swipe up on the app's preview to close the app.
How to restart your iPhone X, 11, 12, 13, or later
- Press and hold either volume button and the side button until the power-off slider appears.
- Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
- To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.
Let us know how that goes.
Cheers!