I had the same problem and tried for a day to get it to work again. Looking into the firewall and stuff which to me is quite confusing. I solved the problem by making use of the app Free Firewall. By installing it I was able to manage all internet traffic, that goes in or out through Windows build in firewall better. So it was as ‘common’ as a firewall problem, but if you don’t know how to go about it, like I did, this worked perfect. Hope this might be of use to someone else!
Is this all about the email I am sure I received weeks ago telling me to update my SDA? Perhaps Steinberg was trying to get ahead of the game. Admittedly it seemed odd at the time, but I certainly had no trouble using SDA when Cubase 13 and Dorico 5.1 came out.