This is a slightly customized version of @BeppeITA's FanHolder to fit @Bubujoe's case. The design is simply perfect for positioning the fan and all the dimensions are perfect.

The height is slightly lower so that it still fits over the small passive heat sinks.

Original FanHolder: https://www.printables.com/model/93987-rpi-234-fan-holder
Desired RPI Case: https://www.printables.com/model/136480-updated-case-for-rpi-4-to-fit-in-40x10-fan-armor-c

I also installed a Noctua 40x10 fan and together with the case, the temperature is perfect.