For sure, i don't think my contribution of 25$ will change anything for this backend, and I don't know anything about programming a backend.
I saw another post wich say about xfilesharing could resolve about a hundred of backend request but I don't know if it's a work in progress because the topic is closed.
I tried to contact Darkibox and the message has been sent to the developpers but if they do it, are we sure the rclone project will add it soon ? I don't see much release 
The UpToBox backend is still in the list in the 1.67.0 version from june,14 but UpToBox is closed since Septembre, 2023.
Just asking, Thanks