Thank you for reaching out to Atlassian Community!
Currently, it's not possible to copy the parent issue values to sub-tasks. We had a feature request that was already closed as "Won't do":
We have another one that is still "Gathering Interest":
Please, click on vote and watch to receive updates about the feature.
As a workaround, you can use add-ons to copy the value of the fields to sub-tasks:
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