I added one user in the readers group to access the Azure DevOps project, the user was able to view the boards and the Work items like below but was unable to edit it due to reader role :-

Now, I visited the Project Settings with my Admin Account > Boards > Team configuration > Areas > Security > View work items in this node > Deny


Now, When I route back to my user who's added to Readers group > The Work Items in Boards are not visible like below:-

To Deny access to Pipelines, Refer the following setting below:-
Go to Pipelines > three dots > Manage security> Deny > View Build pipeline and View builds like below:-


The Pipeline folder is not visible to the user like below:-

References:-
permissions - Azure DevOps deny access to Pipelines - Stack Overflow by Shamrai Aleksander
How to restrict work item visibility/access to the team only in Azure DevOps | by Zaniar | Medium By zaniar