What parts are new when the logic board is replaced by an Apple-certified shop?
Typically you don't know until the repair is complete.

Apple certified shops will enter case noted explaining to Apple what was done and you can ask the shop for a list of what components were replaced.

Apple supplies the parts, so Apple could have sent the repair shop an entirely new logic board or they could have shipped one that was refurbished / repaired / tested. You can't really know unless you physically inspect the part(s) in question.

Service parts are new and/or refurbished whether you have the repair done at the genius bar, Apple Repair mail in service or third party. It's the same pool of parts.

At 500 eu  - you are likely paying for the individual service part to be exchanged, configured and tested. I would ask about a flat rate repair - that would possibly reduce your initial cost and cover any/all issues and not just the main board.

If you can, get a second quote directly from Apple in your country:


https://support.apple.com/mac-notebooks/repair/service