You tube Rewind forward

The Apple TV box generally has 3 methods of rewinding and fast-forwarding.

1. tap left or right to skip in 10 sec intervals,
2. continuously hold left or right to go forward or backward at higher speed,
3. pause, then move the playhead to any other position on the timeline, then resume playing. [My preferred method]

The programmers of the YouTube app may have implemented less than that (2 out of 3), as they see fit for their own app. Some content doesn’t allow fast forwarding (e.g. live content, ads). You may let them know if you want to see changes to the current way of operating: How to contact an app developer - Apple Support