Currently it is only possible to get all issue-created events using JQL filters in Forge. As the documentation mentions only ignoreSelf flag is available:

https://developer.atlassian.com/platform/forge/manifest-reference/modules/trigger/#filter-reference

This is a major blocker for developers to migrate from Connect, as there is no parity with the available Connect filters as described in https://developer.atlassian.com/cloud/jira/platform/webhooks/#restricting-your-events-to-a-subset-of-issues-via-jql

Please consider having these filters implemented to create parity with Connect features.