Dock WD19TBS + Precision 3581 + Bitlocker + external keyboard not working

Hi!

I want to use my external keyboard for any inputs including the Bitlocker-password on startup, because I have my laptop closed UNDER the desktop during work (clean desktop).

My Dock is the WD19TBS.

On my old Dell-laptop (unfortunately I don't remember the product model, it was a 2020/2021-Model), it worked!

But now the new Dell Precision 3581 doesn't recognize the keyboard with the WD19TBS , I can't get it to work!

The Bios-Settings (Fastboot - Thorough    etc.) are all set.

Surprisingly another Dock, the WD22TB4 WORKS!!

I also called the support and got a new replacement-dock (also a WD19TBS), but it doesn't work anyway.

What could be the problem? Is a replacement with a WD22TB4 the only solution?

Thanks and kind regards!

Günther