How to customize data sources in the dropdown box of TFS work item templates? The current situation is as follows:
The options in this dropdown box are fixed. How can I customize this data source, such as the value of the option coming from the interface query.
I thought about implementing it through plugin extensions, but I couldn't find any reference examples.

That is not supported. However, you may add a global list (Define global lists), and add it to your work item type Define pick lists:
Then you may use
witadminto export, modify, and import global lists: Manage global lists for work item types