Hi ,
go to file
Your Bench Name/apps/frappe/frappe/public/js/frappe/list/list_sidebar.html
line NO 20
and replace it with this block of code
{% if doctype!="Sales Order" %}
<li><a href="#List/{{ doctype }}/Report">{{ __("Report Builder") }}</a></li>
{% endif %}
But you should know these lines hide Report Builder for this doctype only not for all doctypes
From role permission manager remove report permission for that doctype
But removing report permission will remove access to all reports in this list,
and what i understand that he needs to remove just “Report Builder” from the list