Here's how you can achieve this using the This can be achieved using existing functionality of Issue Matrix (IM):
Create a separate IM field for sub-tasks.
Specify which columns are relevant to sub-tasks.
Add the new IM field as a column to in the Epic IM field.
The sub-tasks of each issue inside the epic will be are shown on that line as well.
Check out this simple an example of on how it could look looks in the attached screenshot .below:
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Please find Find the below example for reference:
Create your respective fields in the sub-task custom field as shown in the below screenshot.
Create your respective fields in EPIC Epic custom field as shown in the below screenshot.
Please refer Refer to the below gif for reference to achieve your target.
