I went to sync my entitlements for my Master Tier subscription so I could get the Vecna background for my character sheet but I can't sync it and the background is nowhere to be found. I looked all through the backgrounds, themes, etc and wasn't able to find it.

Did you “claim” it?

https://www.dndbeyond.com/claim/source/vecna?icid_source=house&icid_medium=banner&icid_campaign=vecnadossier

Yes I claimed the Dossier.

If there is no button to sync your account entitlements then that means they are currently in sync.

The Vecna backdrops don’t have their own heading, they should be the last four listed under “Subscriber Backdrops” dated “6-22” #s 1-4.

I went back and was able to find it. Thanks for the assistance.