The issue was that only the first Change()
was recognized.
This is because after every change, submit and click the UI is rendered again.
It is smarter to call it the following way:
var ctx = MyTestContext();
var cut = ctx.RenderComponent<Login>();
cut.Find("input[aria-label=Mail-Address]").Change(testuser);
cut.Find("input[type=password]").Change("s3cur3_PASS");
cut.Find("form").Submit();
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