EA_Solaire I tested the Store site just now and still can't login. In Firefox (macOS version), I'm already signed into this site, and clicking Login on store.thesims3.com sends me to http://www.thesims3.com without signing me in. Clicking Login there refreshes the page without signing me in.
I tried this in Chrome as well, where I've cleared all browser data. When I tried to sign into the Store, I was asked for my email and password, then a 2FA code, but then I got the same result: punted to the main site with no login. However, the login process did work because I could sign into this forum in the same browser window without having to input my credentials again.
I'm in the U.S. and am not using a VPN or any adblocking/pop-up blocking/other add-ons aside from what's built into either browser. I did however decline to allow cookies in both cases.