Can't edit content on the homepage, because there isn't any shown in the editor

page templates need to be edited in ‘appearance’ ‘editor’ – then select the file from the list on the right.

you might find the Template Name (not the template file name) under ‘page attributes’ when you try to edit the page
(from your screenshot, i would assume this is ‘Homepage’)

you need to remember/find which file name you gave to this page template.