Activate second iPhone without data transfer

Are you seeing the Activation Lock on the screen that says it is Locked to the Owner? If the phone was properly erased before donating, you can set up the phone as new without transferring any data from your other phone. You have a choice of creating a new Apple Account to be used or if you want the data to be shared with your other phone, you can use the same Apple Account. The options are seen here:

Set up your iPhone or iPad - Apple Support

If you are seeing that it is locked to the previous owner, then you will not be able to set up the phone.

If the donated phone is legit, you will see the "hello" screen when you power up the phone.

Follow the prompts to set up the phone using a different Apple ID. You will have to contact your carrier to set up service with a different phone number.

If you don't see "hello", the phone is probably stolen and you won't be able to set it up anyway, unless you know the person who donated the phone and they are willing to unlock the phone for you.