Think of it this way: they're paying you lots of money to build something boring that has a lot of prior art/research available to you for free. This could be the easiest money maker in your life.
It's not your problem they're hellbent on building a new wheel. They're willing to pay you!
Chances are, you've thought of your own pain points in whatever they've asked you to build and you've now got an opportunity to shine by solving them and demonstrate your expertise.
There is a tool invented lately, that's very good for solving problems, that are well-researched and had been solved multiple times already.
This tool is actually why there is a RAM shortage in the world right now.
Some even say, this tool will replace a lot of workers soon(sic!).
It's not your problem they're hellbent on building a new wheel. They're willing to pay you!
Chances are, you've thought of your own pain points in whatever they've asked you to build and you've now got an opportunity to shine by solving them and demonstrate your expertise.