We have integrated Jira Align and Jira Cloud. Using Atlassian best practices - wherein we have a separate Jira project for features (Jira Epics) and multiple Jira projects for Stories, Defects etc.
Now we have created "Releases" (Fix Versions) in some of these Jira projects (projects for Stories Defects) for tagging of defects, which are integrated to Jira Align.
Would creation of releases (Fix Version) in Jira Projects (projects for Stories, Defects) impact release vehicle in Jira Align? Would these releases would show up in Jira Align?
The fast answer here is this: Use Jira to create and manage the releases (fixed version) needed to for the trains CI/CD needs. Allow the integration to carry those Fixed Versions into Jira Align for visibility and larger coordination.
As each Fixed Version in Jira is specific to its board the integration will bring them over and show all the Fixed Versions in the Release Vehicles (out of the box name in Jira Align). To get one view of all the work in a given Release Vehicle/Fixed Version you need to use the More Actions>Consolidate report
Once you have this working smoothly you can then use the Program Room to track Releases due in a Program Increment, the Roadmap for Release Vehicles, and the lesser known, Release Vehicle Roadmap.
This should point you in the right direction!