I have a trick at my work as a developer to gain hyperfocus on difficult tasks, with 3 simple steps.
Step 1. Prime your brain
Search for content on the internet like youtube videos, Tutorials, articles etc. anything that is somewhat related to the task and interesting to watch and even enjoyable. Your mind needs to latch onto it. Keep doing this and procrastinate until...
Step 2. Take the insipirational exit
At some point your minds interested will peak and your mind wonders how to solve this yourself. Its going to itchband you will not be able to sit still. Take the inspirational exit and jump straight into your project.
Step 3. Its focus time!
You mind is now filled with ideas and you jump into work. You start with the easiest thing and your mind will keep pushing you to finish all those great ideas it got from watching/reading all that content.
Go from easy to hard to stay in the flow state, but this will mostly solve itself.
If everything works out, time will fly and you will have completed the task using your hyper focus. If not repeat Step 1.
This method works best with programming or digital art, but can also be applied to anything else.
Hope that helps some of you.
Cheers
It might be enough to break it down and find bits and pieces that are interesting to you. Things like why do certain tax laws exist, the history of taxation, potential reasons tax laws are so complex, etc. Maybe there are even some videos on different strategies for filling out boring documents that might help.