Hello Severin,
An extension frame for the mainboard was not included in my delivery. I have not been able to find the product otherwise. As a solution, I just screwed on the 6 screws and let the right side overlap.

The expansion frame for a vertical GPU can be bought from Lian-Li itself via Digitec. You can find it under the name:

Lian-Li O11D-1W-3 Mini Riser Card + PCI Slot Bezel - PCIe 3.0

Cost as of today: 69.50 CHF

Hope I could help you further.
Greetings