there are different features you can use Load More button in, like Pro Gallery or Wix Stores, could you clarity which one you are looking for:
https://support.wix.com/en/article/wix-pro-gallery-enabling-and-customizing-a-load-more-button
https://support.wix.com/en/article/wix-stores-setting-how-customers-view-more-products-in-your-product-gallery
If it’s for elements connected to the content manager, you can follow the steps here:
https://support.wix.com/en/article/content-manager-working-with-dataset-actions-for-buttons-and-images#load-more