Welcome to the wonderful world of OpenSSL error messages; they can be mysterious and sometimes incomprehensible even to experienced developers.
In this case, the key lines are:
OpenSSL: error:0906D06C:PEM routines:PEM_read_bio:no
OpenSSL: error:140AD009:SSL routines:SSL_CTX_use_certificate_file:PEM lib
Cannot load inline certificate file
Exiting due to fatal error
The first gives you a clue that it's trying to read PEM data; this is the data format typically used for SSL certificates. The second and third lines make it clear that it's trying to load a certificate and failing. The last line makes it clear that it ain't gonna run unless you supply such a certificate.
It doesn't say here exactly what file it's trying to load, but if you go through all the certificate files you've configured for OpenVPN, checking each of them, you'll probably soon figure out what's missing. There would definitely need to be a server key and certificate, which is the most likely cause of this; there may also be client certificates to tell the server what clients are allowed to connect.
Given a configuration line along the lines of
ServerCert /etc/pki/foo/mycert.pem (this is probably not OpenVPN syntax), you could check to see if the certificate file exists and actually has a certificate in it with
openssl x509 -noout -text -in /etc/pki/foo/mycert.pem
(This will also display useful information about the certificate, such as the identity, who signed it, the validity dates, and so on. Be particularly careful to check the date range for which the cert is valid as that's a common source of authentication breaking.)
Note that if a file has multiple certificates (it has more than one
-----BEGIN CERTIFICATE----- line) this will display only the first one. You can copy the file and edit it to remove the first certificate to display the next one.
This is not at all a Raspberry Pi-specific question but an OpenVPN one generic to any Linux system, so if this answer still leaves you confused you should probably start by checking the more Linux-oriented Stack Exchanges for questions about similar problems.