On the local copy of your website, the currency switcher is not working at all, even without a VPN from the Netherlands.
First, at WooCommerce > Settings > Multi-Currency, I deleted all enabled currencies, as they are not even used on the site.
I also disabled the option "Automatically switch customers to their local currency if it has been enabled".
I proceeded with testing on the English archive page for 4VOO while using the Language URL format "Language in directories" in order to find out if the issue might be related to "Different Domains per language".
According to your WCML settings, all currencies should be available in English, which indeed is the case, but the currencies still do not switch on my test.
I then tested only with WooCommerce and WPML, String Translation, and WCML and it worked as expected.
The issue occurred again once I enabled the plugin "WooCommerce Payments" which further appears to be the plugin that adds a new Multi-Currency Feature directly to WooCommerce and breaks the functionality of WooCommerce Multilingual & Multi-Currency.
I can therefore only suggest to deactivate the WooCommerce Payments Multilingual Feature here: /wp-admin/admin.php?page=wc-settings&tab=checkout§ion=woocommerce_payments
See screenshot.
The issue has been escalating towards our compatibility team and I will keep you updated as soon I receive more feedback from our team.