For iOS WhatsApp, access Settings, and go to Chat Settings, Click on and off to disable the “Save Incoming Media” option.  This will not allow the media to access your Gallery.

For Android phone it is best to move WhatsApp Media files to your storage and then click the folder you don’t want to be accessed by Media content. In order to do this, you can also connect the phone to the computer and check folders or you can allow files explorer to navigate into your device.

While using file explorer on the phone, move to SD card and then WhatsApp and then Media. Click on one folder to rename it. For example, “WhatsApp Images”, replace it by “.WhatsApp Images”. The period introduced in the folder name makes it invisible, and they cannot access Gallery application.