Suggestion, don't use your pinky. I haven't used it for over a decade. Instead, move your whole arm as a unit, and primarily use your index finger. It takes some adaptation, but movement is better than stillness the vast majority of times.

As for the tendinitis, have you tried physical therapy for your fingers? Whenever I've had a stupid day of overusing the thumb with my phone, I wrap the smallest possible elastic band around my thumb, and do some curls. Slow and controlled. The mixture of force, movement and stretching feels great, and the issue is gone.

Here is an example band https://www.decathlon.es/es/p/banda-elastica-5-kg-cross-trai... the important part is that it's really thin and light. It should look like a string, not a flat band.