Make sure the theme is compatible with the block editor

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If you're using an outdated theme that doesn't fully support Gutenberg, you can consider using a block editor compatible theme like Hello Blocks. Or, switch to a default WordPress theme (eg, Twenty Twenty-Five) to check if the error disappears.

Steps to switch themes:

Aller à Appearance > Themes .
Activate the latest default theme like Twenty Twenty-Five .
Open the post or page in Gutenberg and check if the block loads properly.
Make sure the theme is compatible with the block editor when "this block has encountered an error and cannot be previewed" error occurs
If switching themes resolves the issue, you may need to update part time data your original theme or find an alternative that supports the block editor.

3. Check if any plugin conflicts with Gutenberg
Since plugins can interfere with block rendering, disabling conflicting plugins may resolve the issue.

Steps to check for plugin conflicts:

Aller à Plugins > Installed Plugins .
Deactivate all plugins.
Reactivate them one by one and check the editor after each activation.
If the error reappears after activating a specific plugin, that plugin is likely the culprit.
Either find an alternative plugin or contact the plugin developer for support.
To get a hassle-free Gutenberg experience, use a plugin that is perfectly aligned with the block editor and WordPress core. So, you can consider using the GutenKit Block Editor plugin for Gutenberg .