Can I fix my 2021 mazda3 using car parts from previous years (i.e. 2019 or 2020)?

Hello, it's impossible for anyone in this forum to be entirely sure. You'll need to check with your local Mazda dealership parts department to check the specific parts you are speaking of. They can check the part number to see what year's it applies to. If there is a match - then you know you're good.