Adding `remove_theme_support( 'block-templates' )` for site with existing user created template causes error

[andreawetzel]

Description

Removing theme support for block templates on a site that has a pre-existing template added by a user results in a white screen error on the front end.

Step-by-step reproduction instructions

1. Add a new template (either from "Create new template" command in the Page Editor or in the Site Editor > Templates > "Add New Template")

2. In twentytwentyfour/functions.php add the following lines from curating the editor experience documentation:

function example_theme_support() {
    remove_theme_support( 'block-templates' );
}
add_action( 'after_setup_theme', 'example_theme_support' );

3. Reload the website home page and see a white screen.

Screenshots, screen recording, code snippet

No response

Environment info

WP 6.6
no Gutenberg plugin
Twenty Twentyfour theme
Chrome
Mac

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

[carolinan]

Thank you for the report.
I found that only adding the theme support caused the front to show empty pages, I did not need to create a template/part or save any changes to templates /parts.
The page source, when using "view source" in Chrome, is empty.

What is the expected result?
I think it may be an issue with missing documentation, because removing the theme support does not only remove the option to edit or swap templates from the block editor.

It literally removes the support for block templates, so they do not load:
https://core.trac.wordpress.org/browser/branches/6.6/src/wp-includes/block-template.php#L20

In classic themes and hybrid themes that uses theme.json, it removes the template editing options from the block editor and it stops the custom template from loading, loading the PHP template instead.

In block themes there is no PHP template to fall back to, so there is no template to use on the front.

[github-actions]

Hi,
This issue has gone 30 days without any activity. This means it is time for a check-in to make sure it is still relevant. If you are still experiencing this issue with the latest versions, you can help the project by responding to confirm the problem and by providing any updated reproduction steps.
Thanks for helping out.