How to bypass Activation Lock on refurbished iPhone 12 Pro?

When submitting an Activation Lock removal request, it also requires the original proof of purchase. If you supplied a receipt showing your eBay purchase, that would not qualify since you are not the original owner. You would have to try to get that receipt from the eBay seller, assuming they were the original owner.

With Apple denying the request to remove Activation Lock, you are correct the device is a paperweight. In most cases the only way Activation Lock would be removed is by using an original Apple or Authorized Apple Seller receipt for proof of ownership. I have not seen where an Ebay receipt would prove you are the original owner of the device. We always recommend to only purchase from Apple or Authorized Apple Seller for a number of reasons and that is just one of them.

It doesn't matter if you are the original owner or not, what matters is being able to submit the receipt for the sale of the device from Apple itself or an Apple authorized retailer. Unfortunately since you cannot get access to the account set on the device, this means the phone is now pretty much useless to you. That's the danger in buying an Apple device of any kind from a third party unless that party can also provide that original receipt from Apple (they rarely can/will).

Read this section from the very bottom of Apple Trade In - Apple :

"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 Apple 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."

Also, since you mentioned you got the phone for your employee - I'd recommend for future needs that you get in touch with the Apple business team. See the "Get in touch" button on this page: Business - Apple, or visit your local Apple Store. The business team can help with things such as MDM (mobile device management). This will make it a lot easier to give you some control over employee's devices, including being able to easily sign in/out of accounts.

You will want to set up any future phones using Apple Business Manager or Jamf or another MDM, as supervised devices with managed Apple Accounts.

For an intro to the setup:

• https://www.apple.com/business/docs/resources/Managing_Devices_and_Corporate_Data.pdf

For the end user of the device:

• Get started with a supervised iPhone or iPad - Apple Support