I'm not sure how new the Create Document Set action is in Flow - I noticed it today and my admin had not seen it before either, but we are a GCC environment. I was unable to find any documentation aside from this: https://learn.microsoft.com/en-us/connectors/sharepointonline/#create-new-document-set
So, if anyone has used this action before, I'd love to hear about it. I was able to get it to partially work.
I was able to use the action to create a new document set fairly easily, as long as I only filled out: Site Address, Library, Document Set Path, Content Type ID, Title. I was unable to add any metadata. For reference, the metadata fields are identical between the list I'm using to get the information from and the library in which the document set resides. Some of them pull from the same linked list. Some are choice columns that are identical. The fields matched completely between the list and the library, sometimes pulling on ID and sometimes on Value, based on whatever Flow displayed. The one where the field pulls from a linked list, that one failed and gave me a Bad Gateway error. The one that was a choice column worked, but the field on the document displayed as {ColumnName Value: "text"}.
So after two fields effectively did not work, I did not test the remainder, but instead created the doc set with bare bones info, then the next action was Update File Properties, where I added in all the metadata.
Curious to hear if anyone else has noticed this action, tried it out, and what results you've had. It's so much easier than trying to do an HTTP request, for us no-code people.