joseph_mind My phone hasn't been dropped or gotten wet ever since I bought it, nor have any problems with it before the latest update.
Electronic components wear out over time and eventually fail. Batteries wear out, flash storage wears out, screens wear out, DRAM chips wear out. Capacitive touch sensors can wear out, too.
While it is faintly theoretically possible that you are encountering a software problem, for such a (hypothetical) problem to be fixed it would likely need to be reproducible by a developer. As long as (hypothetical) bug manifests itself only on a phone that the developers don't have access to, it's probably unfixable. And, given EOL issues for the 4a, this (hypothetical) bug is not likely to receive a lot of developer focus.
Overall, my personal suggestion is that the most effective way for you to get a working device is to act as if 4a has a hardware failure: get a replacement. I would suggest a 6a or newer based on EOL considerations.
Please note that I do not speak for the GrapheneOS developers.