Update: This issue should now be fixed.
On some PC computers with high resolution displays, there's an issue where you will be unable to click the "Log In" or "Next" buttons on the Create An Account screen. The elements will appear squished together as pictured below.
Zooming in with "Ctrl" and "+" will correct the aspect ratio for the page and correct the issue, allowing you to click the links and buttons.
Zwift Launcher renders these pages using Internet Explorer, but there is a bug related to the display size that causes them to appear incorrectly.