I really couldn't find anybody with this problem so I came here for assistance as my last hope.
I'm trying to create a URL activity with "In Frame" option selected in the Appearance tab, but the result comes back as a blank page.
I don't know what to do, on my other Moodle site it's working fine.
Moodle build (where it is working): Moodle 3.9.1 (Build: 20200713)
Moodle build (where it is not working): Moodle 3.9.1 (Build: 20200713)
I tested some potential causes, maybe the theme was the faulty or the course format, but neither.
Tried to search in forums too, but there isn't even a URL section under Moodle in English > Activities inside the forum..
Thanks for the help in advance!