Already got feedback from TanTan (Vivian).

1. They will conduct an in-depth investigation into the fork issue of the TT-X68.
2. After doing so and finding the root cause of this material problem (if there is any) they will sent out a new and painted fork.
3. From the pictures provided they stated the frame looks ok and should be safe to ride, but checking every mm visually plus doing the "coin" test should be the next step from my side. In any case of noticable damage I should get back.

Lets see...

How exactly are they planning to do the „in-depth“ investigation? Are you going to send the fork back to TanTan for an examination?

In my opinion, the rapid ultimate failure is a significant issue and safety concern and the root cause can not be investigated via photos. I think e.g. fibre volume fraction and resin curing state should be investigated by a laboratory via acid or burn off method and DSC analysis on your specific fork.
However, such analysis would be more expensive than the frame itself…

Concerning your frame, I am not sure I would rely on a „Coin Test“. You crashed with your bike with uncertain und maybe invisible damages to other components, such as the frame. The root cause was TanTans fork, so I think they should at least offer a discount on a new one (or pay for an CT inspection?) after they finished their investigation.

Best regards from somebody who just ordered his first frame from China