Jira will resolve the name to the built in Priority system field and use its values is correct.

When JQL evaluates a query it maps the field name to a single field id and system fields take precedence. Creating a custom field called Priority does not change which field id the name resolves to in queries. The built in Priority system field therefore supplies the values that the JQL expression uses when you run priority = High.

The JQL will match values from both the built in Priority field and the custom Priority field is incorrect because JQL does not merge values from two different fields with the same display name. The query only evaluates the single field id that the name resolves to.

The JQL will fail and show a name conflict error is incorrect because Jira does not present a name conflict error in this case. The system resolves the name to a field and executes the query rather than failing with an error.

Jira will use values from the custom Priority field instead of the system field is incorrect because custom fields do not override built in system fields for JQL name resolution. The built in Priority field remains the source of values for queries that reference that name.

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