Unable to remove the KMS KEY. Need helps

Dear McDs23, it depends. I see two possible scenarios here: 1 - the actions you mentioned have been blocked by SCPs, in which case you can easily solve the problem by updating the SCP policy. 2 - the most common case is when the user accidentally configures a KMS policy that limits itself the usage of the key. In this case, you want to try first to amend the policy by logging into the account as root. If this doesn't help then you would need to raise a ticket to AWS support, they will contact you providing a PIN that you have to provide when contacted over the phone and after that AWS support will fix the problem with the KMS key.

Hope this helps ;)