CTIA-OMTP adapter from Amazon (DE): https://www.amazon.de/dp/B07PVXCLFR?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

DayZ steam community post: https://steamcommunity.com/app/221100/discussions/0/3570700856113781892/

Edit: I finally found the solution! I found a german post on the DayZ steam community page where another user with a Razer headset had the same issue with a not working ingame voice chat. Somebody wrote a comment that there are different audio standards. Long story short...he recommended to buy a CTIA-OMTP adapter from Amazon. With the adapter other players can hear me again via ingame voice chat. If it's allowed to post links, I will do so that other users can read the steam community post or buy the adapter from Amazon.