Thanks for the update.
You were smart to stay in shape at the gym.
I've had this type of hand gripper for years. It has individual press down springs for each of your fingers. They come in a range of strengths. I got mine from Amaz*n.com. Do you have one?
I have full "strength" in my left 4th finger that I incurred the mallet finger deformity years ago. Despite plenty of exercise, I did lose a bit of ability to fully curl my finger at the distal joint after 6 weeks in the splint - but I never notice this interferes with anything. [I am right handed.]