Which customization do you appear to be missing?

For the new lineages, they are grouped in the Race page of the Character Builder under Lineages:

The general background features are not full backgrounds, and so can't automatically be added to the character sheet, although there are a few different ways one couuld go about adding them to the sheet via homebrew tools.

For the Dark Gifts, the first post of the Van Richten's Guide to Ravenloft issues and support thread indicates that these will be available later this year after the implementation of the new Features System:

We don't currently have a way to model supernatural gifts, charms, blessings & boons.

We understand that Dark Gifts are an important part of the Domains of Dread and that our community is keen to be able to use them on their D&D Beyond characters.

We fully plan to support these (this year) with the Features System, but unfortunately this will not be in place for the launch of this sourcebook.

It's also worth mentioning that any character sheet backdrops and frames were pre-order bonuses only, though they may be available again in the future as subscriber perks.