Franck, what style of banjo are you playing? If it is three-finger Scruggs style I don't see how you could bind your fingers together. From what you are describing, especially since you have come back to playing after 20 years, you may have focal dystonia, like me. It has ended my playing, both Scruggs style and clawhammer. You might want to check it out with a neurologist.
I (am trying to...) play Scruggs style. I will look what is a focal Dystonia and I hope I could play my brand new banjo.
Thank you for your answer