Hi Anna Magic,
I’m sorry but this issue is not related to the theme. The code you see is called shortcodes and it is part of your page content, not the theme.
You must have installed the theme on existing website and you were using some page builder plugin (probably https://www.elegantthemes.com/plugins/divi-builder/). Once you deactivated the plugin it left the shortcodes in your page content.
To resolve the “issue” you can reenable the page builder plugin or simply edit your homepage (front page) content.
If you don’t want to display static page as your homepage, and want to display your blog posts there, simply set your WordPress homepage display properly – https://webmandesign.github.io/docs/receptar/#pages