I FOUND THE SOLUTION!!!
After diving into deep of operating system I figured out a possible solution which worked for me:
I had a usbserial.kext laying in /Library/Extensions/ and I figured out that it was also a WCH driver
I deleted usbserial.kext and restarted the Mac again => no success
I deleted CH34xVCPControlDriver.kext and CH34xVCPDriver.kext in /Library/Extensions/ and restarted again
I installed another driver: FTDIUSBSerialDextInstaller_1_4_7 and had to confirm SIP integrity
In system preferences -> security I had to enable access for the FTDI driver and saw another process pending named something with Quinheng
As I remembered that Quinheng has something to do with WCH I ticked this process too and restarted
I installed CH34xVCPDriver.pkg V1.7 again and restarted => no success
I plugged in a CH340G device and suddenly a /dev/cu.wchusbserialXXX port appears in my Arduino IDE and is working with my CH9102 device
Plugging out CH340G device continues /dev/cu.wchusbserialXXX working
Hope that this solution will work for other people too!