If using a Windows PC, and you can't see one or all of your screens to share, consider setting your display's resolution to 1080p or/and disabling any HDR (high dynamic range) on that display.
If using the Electron Capture app, please consider loading that app with Elevated privilege's, which can be done via command line or via right-clicking the app and selecting the option to elevate from the context menu.
If on macOS, please be sure to give your browser system-level access in macOS to access your screen.
If on iOS, there isn't an option available to screen share from within the app, but you can airplay your screen perhaps to a computer, and then window capture that output.
For Android users, downloading the VDO.Ninja APK file will let you screen share on Android, however you can't screen share via the browser.