Redirect all URLs to homepage

Add the following code at the top of your .htaccess file:

# BEGIN redirect to homepage
RewriteEngine on
RewriteCond %{REQUEST_URI} !^/$
RewriteCond %{REQUEST_URI} !\.(gif|jpe?g|png|css|js|php)$
RewriteCond %{REQUEST_URI} !^/wp-admin [NC]
RewriteRule .* / [L,R=301]
#END redirect to homepage

Source: https://eugenoprea.com/code-snippets/wordpress-redirect-all-urls-to-homepage/