I can't remove an activation lock on my iPhone 7 using my Apple ID

Given the lack of detail provided, it’s difficult to say.

Perhaps it’s because “your” AppleID is not the same as the AppleID last used to activate the phone (and which is partially displayed on the lock screen) …

… because the phone was not properly prepared prior to you taking possession.

Regardless, until THAT “other” AppleID owner performs the following steps, the phone will never work for you:

How to remove Activation Lock - Apple Support

There ARE options … but both options require the cooperation of the “locking” AppleID owner.

The design is intentional so as to make the device worthless if stolen.

There are no “workarounds.”

It was all completely “avoidable” IF the prior owner had properly prepared the device for transfer as detailed here:

https://support.apple.com/en-us/HT201351

IF you ARE the “locking” AppleID … then YOU can enter YOUR AppleID password to release to lock.

If you’ve forgotten your AppleID password, follow these instructions to reset it.

If you forgot your Apple ID password - Apple Support