WordPress blocking polling request when signed into Admin

Hence, ajax calls that must be triggered from within the wp admin
panel should be registered via the wp_ajax_{$action} hook, and ajax
calls that are triggered from the frontend and have totally nothing to
do with wp-admin, but are like simple REST interactions of your
platform users with your platform server, should be registered via the
wp_ajax_nopriv_{action} hook, no?

No.

wp_ajax_ is used for logged in users. wp_ajax_nopriv_ is used for logged out users. It has nothing to do with whether you’re in the admin panel or not. It’s only whether the user is logged in or not.