I have already tried everything, also went to ALL folders - also in private…
The videos appear on the camera, but not on the laptop.
The manual may contain the folder in which the videos are saved. (And you missed her.)
AVCHD have the same complex folder structure as Bluray and would have to recognize and mount any DVD / Bluray-compatible hardware and software player. Alternatively, you can / must start the MTS (Media Transport Stream) directly.
Attention, depending on the recording mode, the videos are in a larger color space than REC709 and look "bad".
Sony has software and drivers
http://support.d-imaging.sony.co.jp/support/app/playmemorieshome/de/index.html
https://www.sony.de/bild-bearbeitung-video-produktion-software