In UE5.0 it was possible to paste Tracks from one Animation to another, but from UE5.1 this fails with the message "Can't paste section. No selected tracks to paste sections onto".
The attached project can reproduce this and fails when copying a Button track with a Transform Section to another animation.
Successful pasting of Track into Animation2.
Track pasting failed and show message "Can't paste section. No selected tracks to paste sections onto"
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-175301 in the post.