Copy keyframes from one to another file using just copy'n'paste

Situation/Example of Use case: Made the complete animation in blend file A. Now I need to have special isolated renders so copied the file, renamed it to file B and made some changes in there. Now during the render a repeating issue in the animation is detected, which I've fixed in file A by changing and adding keyframes in one f-curve. When I now want to update the exact same f-curve in file B and try to just select these keyframes and copy and paste it doesn't work. Because file B says there's nothing in the copy buffer.

Please allow copy and paste of keyframes from file to file!

What I would expect?

• Select and copy keyframes in file A using the well known shortcuts or context menu
• Open file B in a new Blender instance (or within the same instance by switching file) and use the paste of the f-curve there.|
• IMO this should just paste the keyframes starting at the position of the playhead

Thanks for considering!