the only problem with that approach is that if it’s just you alone using the domain, that’s already enough to track you. even if you used an anonymous registrar, they might not identify you but they can surely track your traces…

They accept written/scanned proof of identity signed by a municipal office (german here). Basically, show your ID to an official and haven them sign a paper to proof your identity. Also, a friend told me, a LinkedIn Support Member may neither have capacity nor skill to validate a foreign documents authenticity.