As many know, the Raspberry Pi 4 can struggle with high CPU temps and overheating. I've designed a simple fan mount to attach a 30mm fan to your Pi to help cool it! There are a few versions with 2 or 3 screw mounts. There are versions to accept m2 (or #2 machine screw) and m2.5 for the board-mount screws. The fan screw holes are all m3. You'll need a 3v or 5vDC 30mm fan as well. We just had the fan wired directly to 5V and GND but you can write (or find online) a script that will control fan speed based on the CPU temperature.
To connect the fan to the headers, I soldered breakaway female headers with 0.1" (2.54mm) spacing to the fan wires and plugged them in. Make sure you use the correct pins and note the polarity!
See fan options here