I disabled the feat prerequisites because i’m doing some custom lineage, i wanted to take elven accuracy but it doesnt appear in the feats list despite seeing several other race specifics like halfling and dwarven feats. 

Maybe it would be easier to just enable all feats for custom lineage? 

I just tested this and I can see Elven Accuracy on the list of Feats when choosing Custom Lineage if I turn the Feat Prerequisites off.

So - if you can't see it then it's likely that you either:

• Don't own or have access to that feat for the character you're building. If you have access to it normally through content sharing - you can only get it by making the character within the campaign that the sharing is on. It won't work outside the campaign.
• Or the character already has the feat somewhere else. If you've added it to an ASI or directly onto the character sheet via the Manage Feats button on the Features section - you can't choose it again - so it will be removed from lists.

If it's neither of them - link the character so a mod can take a look to see if it's something else.

I just checked on the site and it works fine its the app that i was using and its not appearing in. 

Do you have a jeremy crawford ruling on this because that doesnt make much sense to me, when there is literally a half elf race that still gets access to elven accuracy and tashas wording is any feat for which you qualify so if i have some half elf half dwarf that would in my interpretation have both elf / dwarf feat options but i would think no more than two comboed. Again thats just my interpretation but i don’t see that being any stretch of the rules. 

Regardless of the official ruling, It would be incredibly difficult for them to program all possible combinations of races on DndBeyond for the custom lineage without it getting exceedingly complicated during character creation. Nothing is stopping you from disabling the prerequisite so that your half-elf half-dwarf can take either of the two race's feats. 

Also, here is the Jeremy Crawford tweet in relation to this. The big thing is this "Customizing your origin and choosing a custom lineage are two rules, addressing different needs. One is about making your elf/dwarf/etc. the way you want them. The other is about making a character who isn't mechanically attached to any particular species in the game."
Emphasis added.