You can now sync your favorites with Application Guard Window from Windows Defender

Microsoft Edge version 91.0.831.0 (Official build) canary (64-bit)

you need to enable this newly added flag: edge://flags/#edge-wdag-favorites-sync

and then when you open a new application guard window, your favorites will be there.

Learn more about Windows Defender Application Guard mode (WDAG) and it's security features here:

https://docs.microsoft.com/en-us/windows/security/threat-protection/microsoft-defender-application-guard/md-app-guard-overview

https://docs.microsoft.com/en-us/deployedge/microsoft-edge-security-windows-defender-application-guard