I can't log in my iPhone 8 Plus after changing the password

That is Activation Lock, and that is unrelated to changing your Apple ID password.

Activation Lock tracks the associated password for the Apple ID.

This Apple ID in use here starts with j, and uses the iCloud domain.

If you’re seeing Activation Lock (at all), the iPhone was probably recently reset, which usually means something else is happening here, and which can include hardware problem, ownership transfer, or device loss or theft.

Activation Lock.

To clear an Activation Lock, you will need the password of the associated Apple ID, or the original purchase receipt and matching photo ID and a discussion with Apple Support. If this device was recently purchased and the seller is still available, contact the seller for remediation or for refund. A remote unlock using iCloud is available to the person with the Apple ID holding an Activation Lock, if they’re inclined to unlock this device.

If you forgot your Apple ID password - Apple Support

If you forgot your Apple ID - Apple Support

How to use account recovery when you can’t reset your Apple ID password - Apple Support

Contact Apple for help with Apple ID account security - Apple Support

Activation Lock is a theft deterrent mechanism. A theft deterrent that is easy to bypass would not be much of a deterrent. No, nobody here in the Apple discussion forums can help you clear Activation Lock. Only the current holder of that Apple ID and password, or Apple, can clear this lock. For Apple to clear the lock, you will have to provide a receipt with proof of original purchase and with matching serial number, and provide matching personal identification, or similar materials.

And as purchasing devices with Activation Lock is far too common, also see the following:

The All Too Common SAD Reality of Buying a Used iPad/iPhone

Factory reset.

Best case, that reset clears any lingering effects of whatever happened here.

And to be clear, factory reset does not clear Activation Lock.

Failing that, a discussion directly with Apple Support.

They’ll want proof of ownership to clear any lingering Activation Lock, should that be necessary.

Restore your iPhone, iPad, or iPod to factory settings - Apple Support