For Jira Core and Jira Software we have ACJIRA (https://ecosystem.atlassian.net/issues/?jql=project%20%3D%20ACJIRA)
"The ACJIRA project is the JIRA Ecosystem’s team public project for tracking feature requests and known bugs related to the JIRA API platform. This includes:
- JIRA Core and JIRA Software REST APIs
- Atlassian Connect modules in JIRA"
Where should I create feature requests for JSM API?
I used to create tickets in JIRA Service Desk Ecosystem - Issues - Ecosystem Jira
but it is not possible now.