Optional Features Not Appearing

Trying to add Favored Foe instead of Favored Enemy.

I have Tash’s purchased, I can add things like the Gunner feat and other subclasses. 
Optional Features is available as a dropdown menu, but it says I have nothing available.

Has anyone ever run into this? Any advice?

Likely you're using the 2024/5.5e Ranger class, which doesn't have any optional features (yet).

The optional features from Tasha's Cauldron of Everything are for the 2014/5e Ranger class. You'd need to remove the class you have selected and add the other version instead.