Enable Network and new blogs doesn't look right

Question

I have created in my blog with WordPress 6.2.2 a Network using the subdirectory. I changed the .htaccess as the instruction

<IfModule mod_rewrite.c>
RewriteEngine On
#RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]
</IfModule>

and in the wp-config.php

define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', false );
define( 'DOMAIN_CURRENT_SITE', 'mywebsite.com' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

After that, I noticed some minor issues in the website. When I created a new blog, this one doesn't load the CSS and I have an error

https://mywebsite.com/' because its MIME type ('text/html') is not executable, and strict MIME type checking is enabled.

Also if I want to open the dashboard for this new blog, I get ERR_TOO_MANY_REDIRECTS.

I checked few posts (one of them is this one) but there is not one that explains how to fix this issues. Few of them say it is a theme problem: so, I changed with the same result.