In Wordoress 6.5.3 the error: Posting failed. The response is not a valid JSON response appears when you try to publish a post in WordPress. (Updating failed. Error message: The response is not a valid JSON response.)

I’m running wordpress in a Ubuntu 18.04 machine with Apache 2.4

The debug console:

I’ve tried to apply several of the solutions found in Internet but none seems to work.

• I’ve double check file permissions for directories and files
• I deactivate all plugins
• I rewrote and check .htaccess saving the permalinks settings

I’ve try to deactivate Gutenberg blocks with the plugin Disable Gutenberg or Classic Editor but then I’ve got a Forbidden access page.

My .htaccess is:

# BEGIN WordPress
# Las directivas (líneas) entre «BEGIN WordPress» y «END WordPress» son
# generadas dinámicamente y solo deberían ser modificadas mediante filtros de WordPress.
# Cualquier cambio en las directivas que hay entre esos marcadores serán sobrescritas.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress`

I don’t know what else I can try. Pleas help