I'm a few years behind you (53 this year) and had always struggled with chinups. At my high point at about 35 when I thought I was "in shape", I managed to eke out 3. Then the pandemic lockdowns happened. Several months of using the doorway bar really helped get me to the point that even after a heavy squat/deadlift workout, I can do 3x10 at bodyweight. One technique to try, without the band, is negatives. After your band-assisted chinups, step up to the bar (using your bench or whatever) and hold yourself in the top of the chinup position as long as you can, then slowly lower yourself, fighting gravity. Perhaps 3x5. You'll progress quicker than if you were doing the bands alone.
Great progress all around, Richard. Keep at it!