NextcloudPi Fido2 not possible to add webauthn device

Hi,
IĀ“m using NextclouPi (NC 20.03). I would like to use my Nitrokey for passwordless login. When I klick on ā€œadd web-authn deviceā€ the authorisation popups only for a moment. So itĀ“s not possible to the FIDO2 stick.
Is this a problem of NextcloudPi? IĀ“m additional using another installation of a ā€œnormalā€ Nextcloud. There itĀ“s no problem tu use FIDO2.
Creating a complete new clean NextclouPi (!) installation didnĀ“t help.
Can you help me?
Thanks in advance!
All the best