How to animate bag swing?

Hello! I hope you all are okay.
After many tutorials I made the decision to look for help here. Until someone guides me how I can solve this problem.

I’m trying to animate a bag that has a strap that goes with a small belt on one side. The idea is that when the bag “leaves” from the door, its straps are a little “contracted” by the space between the ramp and the door and then, when the bag “falls” the straps stretch completely, generating tension between the bag and the straps.

The detail is that I have already tried to perform this function with a tutorial for making cables. At first, it seemed like a good idea to me, selecting a vertex and linking it to a hook and parenting the rest.
But I still can’t get the rocking effect I need.

On the other hand, because the strip contains a small ribbon on the right side and I don’t want to remove it, I know that you can’t join a curve to a model, so it’s become more complicated than I expected.

I leave a small image of the idea I had.
If anyone can give me a hint or idea on how I could accomplish this, I would greatly appreciate it.
Thank you very much, I’m still learning and I would love to learn this in a better way.
Greetings.

The way i would go about it is:
Assuming you have a single bone (for simplicity) create one or more shape keys for the bag to bend it the way you like and drive the shape keys’ values with bone rotation.
I uploaded an example: