Browsing PC through phone with adb shell I am connected to my phone from the laptop using wireless adb. After that, I connect my phone to laptop physically with a usb-wire. Now with the wireless adb-shell open, I want to find the wired "connection" and browse my pc through android-phone. (Like open a shared folder on the laptop with adb-shell)

Is that possible and if yes, how? (I want to replicate a similar scenario with my phone so I can connect it to my car-navigation system and browse through the system from my PC using adb-shell).
Not possible. ADB is a one-way channel. Excerpt from help:

When you start an adb client, the client first checks whether there is
an adb server process already running. If there isn't, it starts the
server process. When the server starts, it binds to local TCP port
5037 and listens for commands sent from adb clients—all adb clients
use port 5037 to communicate with the adb server.

To access PC you would have to set up an ADB server on your mobile device, which is currently impossible.