Hi there,
the Theme Editor options is a core function.
If its not showing when you’re logged in as an Admin then its most likely your sites wp-config has:
define('DISALLOW_FILE_EDIT', true);
or a security plugin is blocking it.
NOTE – don’t directly edit the Theme files as any changes you make to them will be lost when the theme is updated. Please use a child theme if necessary:
https://docs.generatepress.com/article/using-child-theme/
The theme has a LOT of apply_filter
functions throughout it – so most changes can be made without directly overwriting files.