Currently for online environments, when Relevance Search is enabled it's no longer possible for individual users to switch back to Categorized Search:
https://docs.microsoft.com/en-us/power-platform/admin/configure-relevance-search-organization#enable-relevance-search
"All of your apps will have the global search experience with the search bar in the header for all model-driven apps in your environment. Individual users won't be able to switch to categorized search."

In certain scenarios users are required to switch back to Categorized Search however this is not currently possible without disabling Relevance Search through Power Platform Admin Center for all users.