The combination in Xerocomellus has never been validly published. The taxon should be referred to under the published name, Boletus mendocinensis, but I will put the taxon under Xerocomellus for clarity.

https://mushroomobserver.org/name/show_name/45102 "comb. prov."

Leptonia/Christian Schwarz:
Now published (5 June 2020)