When using Managed Metadata, the Terms you select aren’t actually stored in the list columns, a reference to them is. This reference is called the term’s GUID. The reason for this is that it allows you to change the term, or move it to someplace else in the term hierarchy, and the column data will reflect that change. This means that when you pull these columns into Power Apps or Flow, the words aren’t in the column, a long code of characters is.
There’s a secret list on every site that lists the GUID for all terms used on the site.
For a term to show up in this list, it must be used, it cannot be just in the term set, it must be selected somewhere on your site.
Access your hidden list here: <Tenant>/<Site>/Lists/TaxonomyHiddenList/AllItems.aspx