Technically, whoever owns the private keys, owns the coins.
I agree that it may be unethical to 'take' them if we assume whoever lost that seed has another copy and might notice.
Hehe. Then Exchanges own many coins because users don't have private keys

. They only have email and passwords.
It's unethical for exchanges to steal users' coins.
Just Kidding.
They do own the coins and they do steal coins; that's actually not even a joke!

I suggest you this thread.
[Blacklist] of unreliable, 'taint proclaiming' Bitcoin services / exchanges.
Back to topic: @easternklaas, I think you got enough bits of advice on ways to get the original owner to notice they lost their wallet.
In case you need help with any of the proposed ideas, don't hesitate to ask for more detailed instructions.
Anyways, just posting the address can't hurt and it may reveal that pursuing the matter any further may be futile (e.g. output may already have been spent), as well as helping with search engine indexing.
Make sure not to share the private key with anyone.
Addresses always look like one of these 3 options.
P2PKH which begin with the number 1, eg: 1BvBMSEYstWetqTFn5Au4m4GFg7xJaNVN2.
P2SH type starting with the number 3, eg: 3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLy.
Bech32 type starting with bc1, eg: bc1qar0srrr7xfkvy5l643lydnw9re59gtzzwf5mdq.
Taproot addresses start with
bc1p, but I highly doubt that you have found such a recent paper wallet - statistically, barely anyone uses Taproot yet.