When trying to start headlander via Galaxy, the launch button gets grey at first. After a few seconds it becomes green again - without anything happening.
When trying to start it directly from the folder via Headlander.exe I get a 0xc000007b error message.

For solving this I tried the following:
- restarting the PC
- verify / repair installation via Galaxy
- Trying to start the game with administrator rights

Please let me know any suggestions how to run this game.

(Raising a support request failed when trying to attach DxDiag file failed due to a wrong file format. I tried .txt and .xml but did not get a hint about what is expected.)

IIRC, .txt. should always be accepted. How large was it? I've submitted tickets with an empty dxdiag.txt before (packaging issue).
Try using your browser to enter the support request rather than Galaxy if you haven't already.

Meanwhile I got the ticket raised. No idea why it was not working the first tries. Thanks.