If you do not receive an update notification for Astra Theme, chances are — the theme folder is renamed.
Changing the theme folder name stops updates from https://wordpress.org/ as the theme folder is used as the slug for WordPress updater.
To verify and fix, follow the steps below:
Login to the FTP of your website and go to: wp-content/themesEnsure you have a folder: astraIf it is something else, rename the folder back to astra (or just reinstall Astra theme)
Renaming the theme folder can cause many problems. WordPress recognizes themes by the folder and it is strongly recommended not to rename folders unless there is intention behind.