Why howdy there pardner! I see you have downloaded and installed Fallout 76. A good choice! However I do not mean to be untoward partner, but did you actually mean to download Fallout New Vegas? It's an easy mistake to make pardner, so I thought I should remind you that Fallout New Vegas is also available on gamepass!
Just go to manage storage and clear that space away and make room for Fallout New Vegas, it's easy! Anyway thought I would just try and help you out there pardner, it's an easy mistake to make. Don't be afraid to holler if you need anymore tips on installing Fallout New Vegas! Happy trails!