Redirect All Pages to Home Page except /wp-admin
# 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://www.eugenoprea.com/code-snippets/wordpress-redirect-all-urls-to-homepage/