The fact that nvidia-smi cannot display the per-process GPU memory usage has zero impact on the use of the GPU for graphics or compute applications.
If you just want to know which processes currently use the GPU(s), nvidia-smi does provide that information under “Process name”. As an example, this is what it currently shows on my system:
+-----------------------------------------------------------------------------+
| Processes: |
| GPU GI CI PID Type Process name GPU Memory |
| ID ID Usage |
|=============================================================================|
| 0 N/A N/A 14284 C ...ore_22.fah\FahCore_22.exe N/A |
| 1 N/A N/A 1464 C+G Insufficient Permissions N/A |
| 1 N/A N/A 2132 C+G ...y\ShellExperienceHost.exe N/A |
| 1 N/A N/A 2996 C+G ...ge\Application\msedge.exe N/A |
| 1 N/A N/A 5904 C ...ore_22.fah\FahCore_22.exe N/A |
| 1 N/A N/A 7736 C+G ...bbwe\Microsoft.Photos.exe N/A |
| 1 N/A N/A 8012 C+G C:\Windows\explorer.exe N/A |
| 1 N/A N/A 8400 C+G ...ekyb3d8bbwe\YourPhone.exe N/A |
| 1 N/A N/A 8480 C+G ...nputApp\TextInputHost.exe N/A |
| 1 N/A N/A 9092 C+G ...artMenuExperienceHost.exe N/A |
| 1 N/A N/A 9988 C+G ...5n1h2txyewy\SearchApp.exe N/A |
| 1 N/A N/A 15204 C+G ...SupportAssistClientUI.exe N/A |
+-----------------------------------------------------------------------------+