Running power to garage. Can't find THWN. Is THHN rated for Wet Locations the same thing?
The wire needs to be rated as and stamped THWN. You need that &quot;W&quot; in there, that designates the wire is suitable for wet locations.  As you know, the inside of a buried conduit must be treated as a wet location.
However it's not a problem here, in fact I don't know if there's any THHN on the market now that's not also rated THWN.
That wire is actually dual rated as THHN and THWN, and the jacket will be stamped with both.  They just have THHN on the label and product description.  You can verify this in the Product Brochure PDF linked on the homedepot page in your post.