B1265dnf Duplex Printing problem after driver update

I recently reinstalled the Dell software suite including printer drivers on my Windows 10 system.

Now duplex printing is not possible. I can activate the checkbox in the printing dialogue but it will print on seperate pages.

Re-installation did not work...

It worked for months and years befor the driver uodate

Windows 10 Pro 64bit

Printer connected via Ethernet

Can somone help ?

Thanks in advance

Sascha