A similar thing happened with stocks. Not so long ago they used to be physical pieces of paper. You could trade shares peer-to-peer and even anonymously by handing over the share certificate to someone in person. For dividends, there was a coupon that you could cut off with scissors and use to claim the income.
Imagine you show up today at a Charles Schwab office with a 1977 Apple Computer stock certificate, and ask to sell it. That piece of paper is theoretically worth more than a Bitcoin (thanks to stock splits). But the Schwab branch surely won’t buy it, they’ll send you away. Getting your piece of paper recognized as stock that you can actually trade in modern systems is a separate process.
That’s how it will be with Bitcoin in 2050. You contact Coinbase’s customer service AI and tell them you have an actual Bitcoin on the chain and you’d like to sell it. They’ll politely redirect you to the compliance department that will inform you that it may take up to six months to verify the provenance of your quaint original Bitcoin that’s not registered in the modern custodial systems - assuming your coin has no history with mixers and other addresses of interest to law enforcement, of course.