Hi there Sébastien, welcome to the forums!
Have you tried with a different camera, maybe a 720p one? I have seen at least one case of a user reporting a 1080p camera to be to much for the RPI4.
Regarding the microphone, if you can share any logs or errors you can get maybe we can help you figure out the cause (running dmesg on the device can usually provide some clues).
Thanks!
Felipe