When building a merged client-server executable with the "Use new architecture for application deployments" checked, the data path directory is actually stored in the lastDataPath.xml file in the directories below:

On Mac:
/Users/{username}/Library/Application Support/{databaseName}/lastDataPath.xml

On Windows:
C:\Users\{username}\AppData\Roaming\{databaseName}\lastDataPath.xml

With the help of this file, even when the client executable is provided an update from the server, the data path stored in that xml file will be the first place 4D will check. Otherwise, you can still hold the Alt / Option key while opening the app and you can change the default datafile path which will automatically update the path stored in the xml file.

If you encounter any issue regarding an executable not remembering the datafile path, make sure the built app has the "Use new architecture for application deployments" checked and try removing the xml file and letting 4D recreate it from scratch.