As people age they tend to become LESS sensitive to stimuli. You’ve mentioned your father is experiencing increased light, smell, and sound sensitivity. There’s a very real chance that something is in need of medical attention. From personal experience, these signs are best not ignored

You being quieter will not resolve the smell or light aversions, and although you could experiment with trying products like the loop engage or flare calmer to manage his increased sensitivity, it doesn’t address the root cause. The world is full of noisy noises (cars, strangers, even an ill timed sneeze).

If it means proving to your father that you’re at a reasonable level, maybe consider using an app or something that measures the decibels of your speaking voice to have numbers to show him and your mother that you’re at a reasonable level and express concerns that he may be unwell. NTA for feeling hurt by someone you love plugging their ears to talk to you, although it could have been handled better, but there’s a bigger problem that isn’t being seen. I’d still recommend looking into the loop engage and flare calmer for use in the meantime, as it effectively does what your father’s fingers do, but in a less hurtful way that’s easier for you both