Hi CazBlak,
Thank you for posting in Apple Support Communities!
Are you attempting to use SideCar and Universal Control at the same time? You should test each separately in order to isolate this issue. Before beginning disable both SideCar and Universal Control.
Then turn on Universal Control using the steps here: Universal Control: Use a single keyboard and mouse between Mac and iPad - Apple Support
Turn on Universal Control
Before continuing, make sure that each device meets the Universal Control system requirements, including that each is signed in with the same Apple ID, and Universal Control is turned on.
On your Mac
1. Choose Apple menu > System Settings (or System Preferences).
2. Click Displays.
3. If using macOS Ventura or later, click the Advanced button at the bottom of the settings window.
4. Turn on “Allow your pointer and keyboard to move between any nearby Mac or iPad.” Leave the other Universal Control settings turned on for now.
On your iPad
1. Open the Settings app.
2. Tap General, then tap AirPlay & Handoff.
3. Turn on Cursor and Keyboard. This setting is available only on iPad models that support Universal Control.
If this functions as expected, disable Universal Control and test SideCar: Use an iPad as a second display for a Mac - Apple Support
If this continues, you'll want to reach out to Apple directly. Depending on your region, you may be able to reach them here: Get Support.
Have a good one!