At the moment, the Jira connector does not support required fields in Jira unless there is a specific connector setting for the field (e.g. Story Creation Requires Team).

Though we have documentation for the specific settings for supported fields, we don't have any general statement stating only system field and specific fields are supported to as required fields.
Due to this we have customers in scenarios, configuring Product custom field sync and attempting to set as required on Jira.

Suggestion:
A note in the Jira Setup section of Jira-integration-setup generally stating something along the lines of
"Only "Jira System Required" and "Fields that have a specific connector setting" that are supported to be set as required on Jira"