On Collections (Beta), we should be able to change the order of the products inside a collection using the feature "Move to Position":

https://help.vtex.com/tutorial/creating-collections-beta--yJBHqNMViOAnnnq4fyOye

However, this feature fails intermittently and does not work properly all the time.

• Go to any collection settings admin: .myvtex.com/admin/collections
• Try to change the order of a Product inside the collection;
• Wait until the product is automatically reindexed with the new order on the collection.

There is no workaround in Collections (Beta), but manually setting the order of products is possible in Collections created through the legacy CMS (Portal) with some restrictions: https://help.vtex.com/en/known-issues/manual-sorting-of-collections-doesnt-work-as-expected--aGTNVDT6LKKoWuSceQWs0