I have purchased all feats from Xanithars Guide to Everything but they do not show up when making a custom race. 

Example: I have made an elf variant and when adding bonus feats Elven Accuracy does not show up in the list of selectable feats.

Furthermore, I can't use any private homebrew feats I make. I can add the trait from the Elemental Evil players companion, Svirfneblin Magic.

Quote from xxpusspounderxx69 >>

I have purchased all feats from Xanithars Guide to Everything but they do not show up when making a custom race. 

Example: I have made an elf variant and when adding bonus feats Elven Accuracy does not show up in the list of selectable feats.

 
This is because racial feats will only work for official races/subraces/variants and will not work for homebrew races/subraces/variants. You will need to remove feat prerequisites in the character sheet preferences to add the racial feat, or create a homebrew copy of the feat and add in your hombrew races/etc into the prequisites section.