If all records are considered as equally relevant with regards to Algolia's default ranking criteria, the engine moves on to any Custom Rankings to break ties. If you do not set any Custom Ranking criteria, the records will be ordered by objectID in DESCENDING order by default. It is not possible to change this behaviour. However, we recommend adding a custom ranking attribute whenever possible.
By default, upon an empty query, the search results will be based on the ranking criteria: https://www.algolia.com/doc/guides/managing-results/relevance-overview/in-depth/ranking-criteria/
If all results match equally for the default criteria they will be ordered by any of the custom ranking criteria you have set on the index:
Here are 2 ways in which you can use a workaround to achieve the functionality of ordering by ObjectID:
1 - You could add a new attribute to your records, and pass the same value of your objectID to it. Then, you could use it for your ranking strategy, and define it as your last custom-ranking criteria. We recommend using boolean or numerical values for the custom ranking. However, if you use string values, please remember that they are sorted by lexicographical order. More information about that: https://www.algolia.com/doc/guides/managing-results/must-do/custom-ranking/how-to/configure-custom-ranking/#string-and-null-or-absent-values
2 - To display records in alphabetical order with empty search, you can use a replica - with the same data in your replica index, you can use different sorting strategies using the sortBy attribute. You may also want to look into Sort an Index Alphabetically.