Yeah the whole filing taxes thing is an epic XY-problem. Governments can make this as easy as a digital signature, there’s zero need for an agent of any kind.
Actually most of the things people use it for is of this kind, instead actually solving the problem (which is out of scope for them to be fair) it’s just adding more things on top that can go wrong.
Seriously. The best solution is not having the problem in the first place. Something something Tao Te Ching.