In Angular 8/9 the default behaviour is to take control of all
<form> elements within the view hierarchy. This can be see by looking at the selector for the form directive.
When the Angular Form directive is controlling a
<form> element it is not possible to do a generic form POST. For instance, if you want to redirect to a third party payment service, which requires you to POST to the server to setup a session, and then redirect the current browser session.
In order to achieve this it is possible to get the Angular Form directive to skip a form by adding the
ngNoForm attribute, as can be seen in the fore mentioned selector.
This isn’t well documented anywhere, but the source code provides plenty of help where formal docs are lacking.