It seems that the update solved it, at least both mics are now working when filming on snapchat !
WhatsApp was already fixed before this update. But Signal is still noticeable quiet when recording voice messages.
As I said, not for me. However at the end its off topic here, as the topic is about video audio, and with my comment I just wanted to find out that those complaining talk about videos.
As the audio in videos should have been fixed, when there are still other issues this should be discussed seperately.