Nginx redirect to php after rewrite

I had this configuration working flawlessly:

# Route for Laravel Backend
location ~ ^/(app|api|sanctum|admin) {
    try_files $uri $uri/ /index.php?$query_string;
    gzip_static on;
}

# Nginx Pass requests to PHP-FPM for Laravel Backend
location ~ .php$ {
    try_files $uri =404;
    fastcgi_split_path_info ^(.+.php)(/.+)$;
    fastcgi_pass backend:9000;
    fastcgi_index index.php;
    include fastcgi_params;
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    fastcgi_param PATH_INFO $fastcgi_path_info;
}

then i wanted to cover every call to the backend under a unique prefix:

  location ^~ /backend/ {
    # Remove the '/backend' prefix and pass the remaining path to index.php
    rewrite ^/backend/(.*)$ /$1 break;

    try_files $uri $uri/ /index.php?$query_string;
}

# PHP-FPM Configuration
location ~ .php$ {
    try_files $uri /index.php =404;
    fastcgi_split_path_info ^(.+.php)(/.+)$;
    fastcgi_pass backend:9000;
    fastcgi_index index.php;
    include fastcgi_params;
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    fastcgi_param PATH_INFO $fastcgi_path_info;
    fastcgi_param REQUEST_URI $request_uri;
}

The problem is that the php backend application is actually reached, but it seems that only the index.php file is delivered without it being able to get the backend routes

[2024-04-03 09:05:58] production.INFO: Global Request URI: /