I just completely performed the described setup again from scratch and everything works. I also checked the policy attached to my build role and it similar to yours.
Some questions that might point you in the right direction.
Which credentials did you use when performing the ‘cdk deploy PipelineStack’ step?
Does the role linked to it have the necessary permissions to read the parameter store?
Which version of the CDK are you using? I am using v1.16.3 (build 8c7f593).
What is the content of the ‘cdk.context.json’ file that is created in your project workspace?