Did you click through quite quickly? While working on some PRs I noticed this issue when I clicked through rapidly. Going back to the start and clicking continue after a second or two allowed the window to render.
Might be your issue 
Windows 10 21h2
Mailspring 1.10.5
This bug still happens sometimes when I close Mailspring without closing an open mail. I’m able to close the white screen and open Mailspring afterwards though
If you’re still experiencing blank white/black screens in 2026, please first update to v1.21.1. If it persists, try launching with --disable-gpu (add to your shortcut/launcher) to rule out GPU acceleration as the cause. Also, if you have multiple monitors with different scaling factors, try running Mailspring on the primary display only to see if that affects it.
If it’s consistently reproducible, the developer tools console (Developer > Toggle Developer Tools) often shows the error that caused the blank screen.