You can find our detailed documentation guidance here https://www.algolia.com/doc/integration/magento-2/how-it-works/shared-catalogs on how to the extension handles the enablement of the Shared Catalog feature.
Please note that enabling this feature significantly increases the size of your records (specifically, the price attribute). If you have complex category permissions or intend to have many shared catalogs, assess the impact on your product indices before enabling the feature.