Although the Dynamic Forms app is not primarily designed to configure templates, you can still use it for such purposes.
Steps
Create a new custom field - Select List (single choice) with template names as options.
Configure values you want displayed or filled. As a condition, assign them to the selected template.
Dynamic Forms for Jira - extended Jira custom field management for Jira CloudDynamic Forms for Jira - extended Jira custom field management for Jira Cloud
Result
In this case, the description will be filled automatically once you select Template 1.
Dynamic Forms for Jira - extended Jira custom field management for Jira Cloud