Problem

As of now there is no option to have the Parent field mandatory on create issue screen.
Since this field is considered as an internal field, there is no way to make it mandatory using the field configuration.

Suggested Solution

Give an option for these fields to make it mandatory through filked configuration

Why This Is Important

This helps customer to avoid workflow validators which makes it complex.

Workaround

Workaround for Company managed projects - creating a workflow with a validator on the create issue transition using the below knowledge article.

• Making the Parent field as mandatory/required field during the issue creation.

There is no workaround for Team Managed project