A friend of mine ordered a 60 EUR PC case off of Amazon.nl, but when receiving it today it turns out it is an entire prebuilt gaming PC valued at around 1400 EUR. in the friends group, we speculated that it's returned product that was processed improperly by Amazon as just the case instead of an entire PC. He powered it on to test if it's a functional computer and made it to the Windows 11 desktop, and from what I understand he's planning to set it aside for a couple months in case Amazon notices their mistake, but he's not planning on contacting Amazon to let them know about the wrong shipment.
I read What to do if seller sends more than ordered? and it talks about excess quantity, but I'm not entirely up to date on whether the Netherlands has a law like this or whether a potential law would cover a situation like this, and the other question doesn't really answer this and is also 5 years old, which might mean the law has changed. I also know that Amazon is such a massive company that they're unlikely to notice this mistake, and that even if they do they're likely to just write it off as shrinkage because of the sheer scale of business they do.
Speaking purely from a legal perspective, can my friend keep the PC while awaiting communication from Amazon, or is he legally required to contact Amazon himself and ask what he should do?