OpenVPN with Certificates Question

Hello Everybody

I am connecting 2 Miktrotik Routers ( Router OS V5.22 ) via a OpenVPN - Tunnel.

On the server-side, I imported a Certificate + Key and configured the OpenVPN - Server to use this Certificate.
On the client-side, I configured the OVPN - Client ( Interface ) to use NO Certificate.
Anyway, the connection is successfully established !

Can anybody tell me why ?
Is the Certificate ignored from the OpenVPN - Server and if yes,
what keys ( encrytion, TLS, … ) are used in this case ?

Thanks a lot !

Manfred