I posted this back in March 2022 about the situation:
Ordered a SYNC 4 APIM, lets see what happens once it arrives! - Ford / Discussion - CyanLabs Official Community
Since then, some of the folks I know who had retrofitted Sync 4 into their vehicles to replace Sync 3 had gone back to Sync 3 because of the limitations of the Sync 4 retrofit. Updates and navigation are still not available for the retrofits, and will not be according to Ford. The Sync system is very different as far as how the updates work for the Sync and nav systems in the vehicle. Ford will not release updates publicly for Sync 4 like they did with Sync 3. Instead, they have settled on using FordPass and OTA to push updates to the vehicles. Dealers can perform the updates with FRDS, but the updates require ESN and VIN verification now with the proper file signing.
That being said, there are some retrofits that will work, such as the new Mavericks, etc., that have an option for Sync 4. This is not officially offered by Ford, but it appears to work. At least for now…