I also cannot download or open Act integration. My understanding is that SQL19 was downloaded as part of ACT Premium for Cloud. ACT onboarding expert tells me that a Microsoft issue prevents SQL server 19 from operating properly.
To me this sounds like a vendor who is not able to support their own product. I would drop them as a hot brick.
Even if there is really is a bug/issue on the Microsoft of things, ACT should help you get it resolved. At least if they want to keep you as a customer.