There are a set of “listed” parts that must be designed by the constructor team. There was a bit of a controversy this year because Racing Point used last year’s Mercedes brake duct design. The part was not listed last year, meaning it was ok then, but it became a listed part in 2020 season. Racing Point was penalized a few points in the standings as a result, but allowed to use the design since they couldn’t unlearn how Mercedes designed the brake duct.