Answer by André Leroy-Beaulieu Castro on 19 November 2020
Hello,
Another way we have found that fixes this issue is to go to the Project Trash of your Jira and permanently delete the Jira Next-Gen Projects that caused the duplicate issue types in the first place.
With this solution, there is no need to set the issue type by ID as there will be no issue types duplicated anymore.
Thanks,
André