I am not sure I understand your problem except that it looks like you need help configuring the Eggdrop IRC bot
I see you got a Let's Encrypt cert which includes all your domain names. That's great. And, your nginx server uses this cert with HTTPS - also very nice.
We often help people resolve problems with common servers. And, we sometimes help with unusual services. I have never seen Eggdrop on this forum and don't have any personal experience with it.
I am posting to suggest trying the Egghead site and their various support options - docs, forum, github. You will find more experts there who know this IRC service and how to configure it. https://www.eggheads.org/
To me, it looks like Eggdrop is looking for a cert.pem in a locarion where there is no such file. That's all I can say/think of based on the information currently provided.
It's unknown how Eggdrop is configured, it's unknown why Eggdrop would require a certificate configured in the first place.
Also, is dhub.chatyour domain or just a "random" IRC server you're trying to connect Eggbot to?
I think it’s commonly supported to authenticate to IRC networks with a client cert, but I think it’s usually a self-signed cert that’s tied to an account. Eg, Using CertFP | Libera Chat
But it’s possible some networks require a publicly trusted client cert.
Dear all, thanks for pointing me in the right direction. I solved the problem by pointing the eggdrop bot to the correct path with .pem files by defining "set ssl-capath "/etc/ssl/certs/" " (not /etc/ssl/ as in the default settings in the eggdrop.conf file).
Eggdrop is a bot to programmatically control an IRC network. At the moment the bot and the IRC server reside on the same host (ie my domain dhub.chat incl subdomains) so TSL-encryption would not be required, but I don't want to open a plain-text port for security reasons. Certification is a prequisit for encryption between client and server connection, AFAIK.
BTW, Eggdrop is a bot not a bouncer (proxy), like ZNC or QuasselCore, which keep a permanent connection with IRC even when a user is logged off so no messages are missed.
I'm still not sure that the Let's Encrypt certificate is really required for your application, but thank you for sharing your solution publicly so other people may be able to benefit from it in the future.