I cant sign out from icloud

I found this to be helpful:

(don't go to icloud to sign out, just your account and scroll down)

If you use iOS 10.3 or later:

1. Go to Settings > [your name].
2. Scroll down and tap Sign Out.
3. Enter your Apple ID password and tap Turn Off.
4. Turn on the data that you want to keep a copy of on your device.
5. Tap Sign Out.
6. Tap Sign Out again to confirm that you want to sign out of iCloud.

Selling/Giving Away Device

Why not?

Note: You can only sign out with the correct Apple ID & password that iCloud account is registered in, you cannot use any Apple ID & password to sign out.