Apple Remote app does not function correctly on my ipad6

What is your model Apple TV box? Identify your Apple TV model - Apple Support

Or are you using it with the Apple TV app on an AirPlay-enabled smart TV?

The back button is supposed to go back one menu (up one level), like the previous screen.

The TV/Control Center button is for use with Apple TV box (4th generation or later).

The CH up/down button(s) are for select TV provider apps that support these buttons, to go up or down the channel list.

The blank touch area (middle) is for swiping or tapping navigation in the four directions, and the center tapping for selecting/​confirming a highlighted option.

Control Apple TV with iOS or iPadOS Control Center - Apple Support

Do both devices run the same version of the system software (16.2)?

The on-screen buttons for subtitles and skip-10-sec forward or backwards are contextual, and will only appear when the Apple TV box is playing something that these functions can apply to.

If your issue is different, then please elaborate.