Are computed values stored in 4.x ?

No, values are computed on load/display, and cached with the entity.

Are they visible to Search API?

Yes.

The module https://www.drupal.org/project/date_recur_search_api → uses a computed field which Search API then uses to filter and sort by.

The computed value is there any time the field is accessed.

Automatically closed - issue fixed for 2 weeks with no activity.