Astra theme version 1.0.18 introduces a new option in the layout settings which offers you control the visibility of the featured images.
The options are provided for Blog / Archive pages as well as Single Posts and can be found in the customizer on locations as below:
Customizer – Blog – Blog / ArchiveCustomizer – Blog – Single Post
You can drag & drop the labels to switch the position of title & featured image; or simply click on the eye icon and disable it.