This members-only tutorial provides the steps to limit Oxygen's Search Form component on single and archive pages of a CPT to only the entries of that post type.
We are going to use the get_search_form filter hook and alter the default search form's output to add a hidden input field for showing posts of a specific CPT.
After implementing this, visitors can use the same search form to search sitewide on rest of the pages and search entries of a CPT (like projects or portfolio or testimonials) on CPT single and archive pages.