In Footer Custom Text, a user can add any HTML content. Furthermore, Astra offers some helper strings that can be used to place some useful dynamic content, such as the current year, or title of the website.
More information below:
[current_year] -> This String prints Current Year. [site_title] -> This String prints Current Site Title. [theme_author] -> This String prints Theme name with It's author link.
HTML in Custom Text:
Copyright © [current_year] [site_title] | Powered by [theme_author]
Copyright © 2020 Your Site Title | Powered by Astra
Note: Above mentioned strings are predefined constants in theme. They will not work as shortcode when used with page/post content.