Hello. To answer some of your questions…
Yes there are indexes on all collections ootb which are:
All Wix collections are created with 2 indexes:
-
_id ascending
-
_createdDate descending, _id descending.
as referenced from this article: https://support.wix.com/en/article/velo-indexes-and-wix-data-collections
You may create up to 3 regular (or 1 unique) indexes on your collection which you can also read more about at the above linked article.
Here is another article about how to set them up: https://support.wix.com/en/article/content-manager-adding-an-index-for-your-collection