The “Show Bulk Selection” setting enables a checkbox column in the variation table, allowing customers to select multiple variations at once for bulk actions, such as adding multiple variations to the cart simultaneously.

When this option is enabled, each variation row includes a checkbox, and a “Bulk Add to Cart” button becomes active, streamlining the shopping process for customers who want to purchase several variations in one go./

Before enabling this feature that time it did not show the bulk selection checkbox.

After enabling this feature bulk selection checkbox is shown for every variation in this variation table.