If you are still running a version prior to 5.5.2 on macOS Big Sur, the auto-update mechanism may be broken. Users are advised to download the update manually from the official website to restore functionality.
If you want to know more about the latest version (Default Folder X 6) or need help with a specific feature like setting up folder sets, let me know! Big Sur « St. Clair Software Blog Default Folder X 5.5.2
: Syncs Open/Save dialogs with currently open Finder windows. If you are still running a version prior to 5
: Improved the efficiency of tracking changes in folders synced via cloud services. 📁 Core Functionality Default Folder X 5.5.2
: Resolved issues where the "Open" and "Save" dialog toolbars would fail to load after the version 5.5 rollout.