keybase.io login fails on Microsoft Edge Chromium

Using Microsoft Edge Chromium 81.0.416.64 (Official build) (64-bit) on Windows 10 1909, I'm not able to log into the https://keybase.io site using username and password or using the Settings > Your account > Open Keybase.io in Browser button in Keybase Windows Client. When I try, the page loads, but the Login button remains, and the site continues to behave as if I am not logged in.

I have tried disabling all Extensions. Changing the default browser to Google Chrome and using the login button in the Windows Client did work as expected.

Start by reproducing login at keybase.io in Microsoft Edge Chromium 81 on Windows 10, using both the username/password flow and the Windows Client's “Open Keybase.io in Browser” button. Compare the behavior with Google Chrome; done when Edge completes login and the site recognizes the authenticated session.

Written by the indexing model from the issue text.