Sidecar not showing full screen on Ipad

Hi Macisback100,

Thank you for participating in the Apple Support Communities. We understand that your iPad will not show a full screen resolution when using Sidecar. We recommend making sure everything is set up correct by following the steps in this article: Use iPad as a second display for your Mac.

"Sidecar requires macOS 10.15 or later and iPadOS 13 or later on supported models.

Set up Sidecar

1. Make sure you’re signed in with the same Apple ID on your Mac and iPad.
2. Use one of the following connections:

• Wireless: Make sure you’ve turned on Wi-Fi and Bluetooth on your Mac, and you’ve turned on Wi-Fiand Bluetooth on your iPad. They need to be within Bluetooth range of one another (about 33 feet or 10 meters).
• USB: Connect your Mac and iPad using the appropriate USB cable.

3. On your Mac, do one of the following:

• macOS Ventura: Choose Apple menu  > System Settings, click Displays , click , then select your iPad from the list below “Mirror or extend to.”
• macOS 10.15 to 12.5: Choose Apple menu  > System Preferences, click Displays , click Add Display, then select your iPad from the list below “Mirror or extend to.”"

If the issue persists, Contact Apple Support for further assistance.

Take care.