So, the problem is:
When releasing a version, i want to automate creation of Confluence page with version name (that already exists in Automation library), BUT i want to add auto-generated Release notes to that Confluence page, automatically.
Is there a way to do that?
Perhaps you could setup an Automation rule in Jira that is triggered "When: Version released" then the action would be to "Send a web request" which you would use to call the Confluence Cloud REST API to create the page as you require.
Confluence Cloud REST API: https://developer.atlassian.com/cloud/confluence/rest/intro/
@Zeljko Abas Jira's native automation is one possibility that you could explore & as suggested above look at the Confluence integration.
If you are open to using apps, you can look at the release notes apps available on the marketplace. And if your needs are limited, you can look at the free version of Automated release notes app that my team develops.