It appears that the former action method used to create Jira issues, called Create New Issue, within Power Automate has been deprecated.
It has been replaced by Jira Create New Issue (V2). However, this new action does not support the creation of SubTasks.
I opened a ticket with Support, but they say to use the Deprecated action, which is not available in the pick list of Jira actions.
If I do not edit the Flow, the deprecated action works fine, but as soon as I try to edit the Flow, Power Automate throws an error (see screen shot):
Field 'parent' of type 'issuelink' is not supported. More diagnostic information: x-ms-client-request-id is '8DB53260...
Hoping this is an oversight and not by design. And that it gets fixed soon. As it is, any Flow that tries to create subtasks cannot be edited or changed.

