Hey @ThomasBorowski - thanks for flagging this. I did some digging into this and spoke with my colleague Kyle who looked into a similar question here the other day:
Right now, we don’t have plans to expose the VAT/Tax IDs on the customer object in the Admin API, but I will set up an internal feature request report on your behalf - it does look like this is a really desired feature (for good reason for sure), so more than happy to do that so we have that noted on our end.