Error editing Learning Mode templates

[renatho]

Steps to Reproduce

There are 2 ways of reproduce the same error:

Without a bock-based theme:

1. Activate Twenty Twenty-One theme (not block-based theme).
2. Go to WP Admin > Appearance > Editor.

With a bock-based theme, but with the theme styles disabled:

1. Activate Twenty Twenty-Two theme (block-based theme).
2. Go to WP Admin > Sensei LMS > Settings > Courses.
3. Disable the option "Enable theme styles".
4. Go to WP Admin > Appearance > Editor > Browse all templates (this option appears when expanding the "Home >" in the top bar).
5. Click on "Lesson (Learning Mode)".

What I Expected

To be able to edit the Learning Mode templates.

What Happened Instead

I see the following error:

PHP / WordPress / Sensei LMS version

PHP 7.4 / WP 6.0 / Sensei LMS 4.5.1

Browser / OS version

Chrome

Context / Source

Maybe this stopped working after this change: https://github.com/WordPress/gutenberg/pull/38655 But it needs to be investigated.

[renatho]

It's maybe (maybe because before it was just happening in WP 5.8) duplicated to https://github.com/Automattic/sensei/issues/5083.