Got the riven mask as a triumph reward and saw how stupid it looked and wanted to put it on... except it's not there? Is it maybe for a different class? :
Destiny 2 - How To Get All Festival Of The Lost Masks -
Destiny 2 Festival of The Lost Masks & How to Get Them
Destiny 2' Festival of the Lost 2020 Guide: Get Masks, Cipher Decoders & Candy