I guess I'm simply too stupid, but I've been looking for docs to set up an OpenVPN-Server (not client!) using the Gnome NetworkManager in Centos 8.1.

I need to set up a site-to-site OpenVPN between a remote Cenos box,which is also a gateway to a central pfSense box.
I sucessfully managed to set up OpenVPN lines when the Centos box is the client and the pfSense box is the server, but in some cases I need itthe othe way round as the Centos box has a fixed IP-address and some of the pfSense-boxes have changing adresses.
I have found some scripts scrips to do the job, but the all use tls-certs for auth and I'd rather use pre-shared keys (the default in pfSense for site-to-site VPNs).
So can some kind soul point me into the right direction on how to convince either Gnome NetworkManager OpenVPN-plugin t create an OpenVPN server instance instead of a client instance or how to manually set up a site-to-site OpenVPN using pre-shared keys?
Thank you!