discreat gpu is idle and when i play games gpu is also not working in predator helious 300 PH315-51

From nvidia control panel

• Preferred graphics processor (Only on systems using NVIDIA's power-saving GPU technology.) From the options in the list box, you can specify to  Use high-performance NVIDIA processor for maximum performance or for decoding all video played on displays connected to the integrated graphics. You need to select game.exe file and select High performance Nvidia processor

Widows graphics settings

•  set the default GPU for your application or game, you'll need to associate your games with it so your computer will know which GPU to use. (by deafult the option set is Let Windows decide)
• From Start Icon type "Graphics Settings" and Click the results from system Settings
• Click Desktop App.
• Browse your application or game.exe file. If your application is not on the list, you will need to browse for the folder where the .exe file is located.
• Clickon the application name/icon.
• Click Options.
• Set the application to High performance Nvidia GPU
• Click save.

Open device manager then Expand display adapter and post screenshot of devices that appears

First confirm you are using these settings in nvidia control panel-

Step 1. Right-click on any empty space of your desktop and select NVIDIA Control Panel.

Step 2. In the left panel, go to Manage 3D Settings > High performance NVIDIA processor > hit Apply.

Step 3. In the left pane, hit Set PhysX Configuration > select your dedicated GPU > hit Apply

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Second Important thing to ask did you have Intel storage driver intalled in your laptop?.

Backup your data and perform clean factory reset. You need to select remove everything.

With clean windows update everything using windows update then try to play your games without download driver from any other website.

Completely update your windows then install Game and play. (CHECK IF DGPU WORKING, performance may be bad because we didn't updated nvidia driver to newer but first by playing games check if dgpu becbecome active while playing) (Don't forget to get game.exe on high performance in windows graphics settings first)

Is your laptop is under warranty? Also check device manager for any error