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First of all let's clarify: if you turn off only this option and regenerate the .htaccess file does it work?

If not, stop reading, let me know. We will need to go through some other debugging first before circling back to what I am writing below.

Otherwise, check your site's configuration.php file. There's a $live_site line which probably reads something like that now:

public $live_site = 'https://autopot.nl';

This means that when you access the non-www domain (autopot.nl) the .htaccess file tells your browser to visit the www domain name (www.autopot.nl) BUT ALSO that as soon as you visit the www domain (www.autopot.nl) Joomla itself tells your browser to visit the non-www domain (autopot.nl), thereby creating an endless loop.

Change it to read

public $live_site = '';

Now you can use the non-www to www redirection since Joomla won't be trying to override what the .htaccess file does.

IMPORTANT CAVEAT: You have to completely quit your browser (including any tray icons, if you're using Windows) for your browser to see the new redirection settings: browsers cache redirections while they are still open.