Accessing a webservice/website via IP with https eg. https://x.x.x.x/
the browser shows that the connection is not secure.
Is the connection actually secure/encrypted or not (more secure than http)?
The problem is likely that the certificate is for a domain name, not the IP. So, when the browser checks to see if the certificate matches the domain, it doesn't.
The connection is encrypted, that's not the problem, but you no longer can be assured that it has been encrypted by the party you hope is doing the encryption (the site you were aiming to connect to). So, it can be possible that someone can sit in the middle of your connection and read or modify the traffic.