I have not tried uninstalling the game yet. I was hoping to find a solution that didn’t require uninstalling due to bandwidth limits, but it wouldn’t be the end of the world if I had to.
A VPN doesn’t change the problem, and a different computer on the same network doesn’t have the problem.
I also tried uninstalling the launcher and deleting the cache which had no effect. As well as launching the game directly from the folder bypassing the launcher, and that also had no effect.
It’s worth noting, upon opening the game for the first time the game automatically logs me into my main account (let call it account A). Account A is the account logged into the Blizzard app. However if I log out of that account I immediately get the authentication screen, and I get logged into a different account (account B) with no way of entering a different email/password.
So when I open StarCraft, I get the authentication screen, and I get logged into account A. If I press cancel, or if I log out of account A, I get the authentication screen but I am then logged into account B.
Here is what it looks like
Pressing the cancel button makes the authentication popup briefly disappear and then reappear. The username and password box never appear, when the popup disappears that area is just blank until the authentication popup appear again.
I tried to make all this coherent, but I feel like it’s still a bit of a jumble of information, so let me know if you need anything clarified.
Not sure if it matters but I’m running Catalina 10.15.5 on a 2016 MacBook pro.