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If you have changed your ID or password, have you followed the steps in this article?

What to do after you change your Apple ID or password - Apple Support.      

Where are you trying to sign in? Error message(s)?

Could this be your problem, an updating Apple ID settings problem? Note that Apple is aware of this problem, but there is no definitive solution yet.

And note that some have solved the problem by signing out ofiCloud, restarting their device(s), and signing back in. 

See these documents:

Updating Apple ID Settings https://discussions.apple.com/thread/251076026

Update Apple ID settings iphone https://discussions.apple.com/thread/251180098

Updating Apple ID settings stuck https://discussions.apple.com/thread/251262316

Getting a message to Update Apple ID Settings on iPhone, iPad, or Mac? https://appletoolbox.com/update-apple-id-settings-on-iphone-ipad-or-mac-after-changing-your-password/

How Fix Update Apple ID Settings If It Won’t Go Away https://techzillo.com/update-apple-id-settings/

You also may want to use the support options below in dealing with your problem.

Get a call from Apple support to help solve your problem using this

link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

Apple ID Support https://support.apple.com/apple-id

Apple ID account security for country-specific and region-specific help https://support.apple.com/en-us/HT204169

Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option.

Is this what you tried and then had the problem you mention? Go Settings > iCloud > Account Details > Security > Change Password

Have you tried signing out, restarting, and then signing back in?

You are welcome.