I’ve set up a subfolder multisite.
Main site: https://cs-amx.org/
Subdomain site: https://cs-amx.org/chypre

You see the maintenance screen is well displayed on the main site, but not on the subdomain site.

All the themes and plugin files lead to a 404.

For example, cs-amx.org/chypre/wp-content/plugins/maintenance/load/style.css doesn’t load.

But cs-amx.org/wp-content/plugins/maintenance/load/style.css works well.

The admin panel at cs-amx.org/chypre/wp-admin/ works, though.

Here’s the content of the .htaccess file:

# BEGIN WordPress
RewriteEngine On
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]
# END WordPress

Any idea?