Hi, to use a tag in a tag policy it needs to be a governed tag rather than just a general tag. IF you just create it using Set tags UC sees it as a informational tag rather than a governed tag. If you use a CREATE tag statement to create it then you'll have it as an option in your policies.  Governed tags must have a tag policy which specifies the allowed list of values, this prevents users being able to put any random value against it and threfore is why it's used for ABAC. Docs on Governed tags here https://docs.databricks.com/aws/en/admin/governed-tags/

I hope this helps!