If the Google Drive fails to sync content between your Galaxy S9 and your computer, then you can follow the instructions in this post and try to fix the issue.
Most times the "Google Driver Sync not possible" errors are due to bad internet connections, or your phone is not using the Wi-Fi connection and you've set the "sync only when using Wi-Fi" option for your Galaxy S9.
First you have to make sure that you're logged into your Google account on both the phone and your computer, then make sure that the Sync options are enabled on both devices. After you are sure that these are all working you can continue to the tutorials below.
Reinstall Google Drive Backup and Sync app on both the phone and PC:
As the title says, you have to uninstall the Google Drive Backup and Sync on both devices. Make sure to install the apps and then go to your phone's "Accounts and Backup" options in order to enable the Sync function for Google Drive.
Go back to your PC and launch Google Drive, set it to sync with the same Google account that you're using on your Galaxy S9. Test the Sync function by creating a file on your phone and then see if it is added to your computer's Drive folder. If the sync is fixed you are done with this post and you can use Google Drive Sync once again and backup all your important phone data.
Force stop Google Drive app and re-launch it to test Sync function:
You have to go to Settings> Apps> Google Drive and use the "force stop" option and stop the app from running. After the app is stopped you will have to open it again and verify if that has fixed the app.
Clear Google Drive app cache and app data:
Another thing that you can try would be to reset the Google Drive app altogether, as some of its settings or system installation files might have gotten corrupted. Go to Settings> Apps> Google Drive> Storage and here you have to tap on both the "clear app cache", and "clear app data" options. Confirm the process, then re-launch Google Drive and reconfigure it in order to be able to use it once again.
Wipe Cache Partition of Galaxy S9 using Recovery Mode:
The Cache Partition contains all the data your Galaxy S9 has stored for each app and settings you had added and changed since you first bought the device. By wiping the cache partition you will force your Galaxy S9 to relearn all the installed apps settings and other data these require to run flawlessly. Here's how to wipe the cache partition on Galaxy S9 from Recovery Mode:
- power off the device.
- press and hold Volume Up + Bixby + Power buttons at the same time.
- release the buttons when the screen turns blue and wait 30 seconds for the Galaxy S9 to load all the Recovery Mode options.
- select 'wipe data/ factory reset' and confirm.
- reboot the phone after the process is done.
These were all the steps that you had to take in order to try and fix your Galaxy S9 Google Drive Sync problems. If you need more help with these you should tell us in comments below, but make sure that you list all the issues and steps you took, so that we will be able to easily come up with a working solution.