Explanation:

Step 1 - Requirement
You want to create a custom sensitive info type named Sensitive1.
This SIT will be created from a document fingerprint of Template1.docx.
You then want to use Sensitive1 in DLP policies.
Step 2 - Where do you create custom Sensitive Info Types?
Custom SITs (including document fingerprinting) can only be created in the Microsoft Purview compliance portal.
They cannot be created in the Exchange admin center, SharePoint admin center, or directly in PowerShell.
Answer for creation: The Microsoft Purview portal
Reference: Create a custom sensitive information type with document fingerprinting Step 3 - Where can custom Sensitive Info Types be used?
Once created, custom SITs are tenant-wide and can be used across all workloads that support DLP:
Exchange email
SharePoint Online sites
OneDrive
Teams chat and channel messages
In the table, the DLP policies are:
DLP1 # Exchange Online email
DLP2 # SharePoint Online sites
DLP3 # Teams chat and channel messages
Since Sensitive1 is a custom SIT, it can be used in all three policies.
Answer for usage: DLP1, DLP2, and DLP3