
Hi Ted, thank you for posting in the Q&A forum.
I can reproduce this behavior in my SharePoint Server 2019 environment. It seems to be the default behavior for SharePoint 2019 since it happens in all document libraries on all sites, which is not fixable from our end.
I have also tried using PowerShell to set this field as Read Only, but it does not work for this field either.
I am a bit regretful that I was not able to help you much on this.
In this scenario, I would propose a new support ticket to be raised to have a dedicated Technical Professional to support you from there. The contact number for your region could be easily found from below website, you can simply refer to the Customer Service Representative and he/she will be glad to help you with creating a new ticket.
Global Customer Service phone numbers
https://support.microsoft.com/en-us/help/4051701/global-customer-service-phone-numbers
If an Answer is helpful, please click "Accept Answer" and upvote it.
**Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread. **