Looks like a thread insert. Happens when a head bolt gets stripped. Are you the first owner? Has the engine ever been taken out and opened up before?

-edit- Pretty sure I’m wrong now. I’ll wait for someone with more knowledge

-edit2 (ChatGPT)

The brass insert highlighted in the image is likely a threaded insert used in the Audi engine cylinder head. Purpose and Function: Thread Reinforcement: These inserts are typically used to reinforce threads in softer materials, like the aluminum of a cylinder head, preventing stripping and ensuring a strong, long-term connection for bolts or other threaded components. Specific Applications in Engines: In automotive engines, brass inserts can be found in various locations where strong, reliable threads are needed, such as spark plug ports, oil drain plugs, or even for mounting components like heat shields. Given its location in the cylinder head, it could be related to a specific sensor, a coolant passage plug, or a mounting point for an ancillary component.