For now the best solution to use the Magento position attribute to sort your results is to use the Category Merchandiser. This will allow you to promote items for specific categories, though indeed it is separate from the position attribute.
If you want to use the position attribute to sort your items, this is possible with the following steps, but please note that this means that each item will need to have a single position attribute, and you will not be able to vary the position of an item depending on it's category:
1. Add the position attribute via a php code block hooking into the indexing, as presented here: https://www.algolia.com/doc/integration/magento-2/guides/transform-indexed-attribute/?client=php
2. With the custom observer in place, the catalog needs to be re-indexed in order to for the changes to take effect. Read more about (re)indexing here.
3. Set up your Algolia integration to sort on the position attribute, as presented here: https://www.algolia.com/doc/integration/magento-2/how-it-works/indexing/?client=php#sorting-strategies
The only other option would be to write a script using the PHP API client to create rules for category positions with the same rules context pattern that is being used for the Category Merchandiser.
Last reviewed 29-04-22.