How to bypass Activation Lock on iPhone 11 without original owner's details?

If you see a "Locked To Owner" message or one referring to Activation Locked (iCloud locked), read this Activation Lock removal article --> How to remove Activation Lock - Apple Support To remove the lock you will need either:

-The account information that set the lock.

OR

-The original sales receipt from Apple itself or an Apple approved vendor. Other ways you may think might be “proof” of ownership or purchase, such as having the box, or a receipt from a third party vendor such as Ebay, will likely not be acceptable by Apple. Apple may have no way of verifying the authenticity of other methods. If you have an acceptable receipt, ask Apple to unlock the device —> https://al-support.apple.com/#/additional-support

If anybody tells you that you have to be the “original” owner, they are incorrect. As long as you have the original Apple receipt (which may well not have any personally identifying information on it) you are okay.

If it is asking for an account that is not yours, take it back to the person from whom you received it. Get them to do the things in this support article or ask for a refund --> https://support.apple.com/HT201351 There is no way to discover the owner of a device unless they left a message to display on the device when it is turned on, or the person who gave you the device knows them. Note that the device cannot have Lost Mode set on it. If your device has been taken over as a result of you having entered a scammer’s Account then the scammer may have set Lost Mode too and the device is lost to you.

Return or recycle the device if you cannot unlock it; it is useless to you. From the very bottom of https://www.apple.com/shop/trade-in :

"Does Apple offer recycling?

Yes. Apple Trade In lets you recycle any Apple device (including devices from Apple-owned brands) at any Apple Store and on https://www.apple.com/ for free. That includes your batteries and old electronic products as well as free, on-demand packaging recycling for our commercial, education, and institutional customers. When we receive your device, it will be thoroughly inspected to determine if components can be recycled or reused. Whether recycled or reused, all activities relating to the processing of your device will be managed in an environmentally responsible way."

When considering future purchases read these:

https://discussions.apple.com/docs/DOC-250001038

https://support.apple.com/104999

You can't. You need the owner of the account to release it or you need to be the original owner with the original receipt. Your only options are to find the seller and get a refund or recycle it.

lobsterghost, a frequent poster here, has written an excellent tip on buying second-hand Apple devices.

The All Too Common SAD Reality of Buying … - Apple Community

You don't bypass the Activation Lock (anti-theft lock). You cannot remove it, we cannot remove it, and Apple will not consider removing it under the circumstances you outline. (Neither will Apple tell you contact information for the owner whose Apple Account is logged into the phone.)

Since the "someone" who sold you the phone has apparently "disappeared", that would seem to throw a wrench into the idea of returning the phone to get your money back.

Turn the phone over to the authorities, with the information you have on the seller, or recycle it responsibly. It is – and will remain – a "brick".