My used phone is locked by a Google account. How can I unlock and use it?

I recently bought a used Samsung Galaxy S21. The seller performed a factory reset in front of me and let me inspect the device. However, when I took it home and restarted the setup process, the system asked for the "Google account previously associated with this device." I don't have any information about this account, and I can no longer contact the seller.

Now I'm stuck on the verification screen and can't complete the phone setup, even though the phone itself works fine and has no physical damage.

I tried the Google account recovery process, but it requires the original email or phone number. I also tried entering Recovery mode to reset it again, but after restarting, it still asks for the same account.

Besides the original purchase receipt, are there any other ways to prove legal ownership of the device to Google or Samsung? If you have successful experience dealing with similar situations or know of any currently viable solutions, please share! Thank you very much!