@KamilParzyjaga and @emre.toptanci,
I confirm there are no published APIs for the roadmap features.
I know the thread about Deprecation of the Epic Link, Parent Link and other related fields in REST APIs and webhooks is long; however, it seems to indicate an intent to pull the necessary APIs into the Jira Platform, rather than to have a separate set. The parent fields is proof the team is working in that direction, albeit slowly.