How to configure auto-download
By default, WhatsApp will automatically download images over your cellular connection to provide you with quick access to your latest photos.
To configure automatic photo, video or audio downloading, simply go to WhatsApp > tap More options
Here you can choose when WhatsApp will automatically download media.
Note: WhatsApp is joining other services in reducing potential mobile network congestion during the coronavirus (COVID-19) pandemic. To help improve these mobile network bandwidth issues, we’ve disabled auto-download for documents, videos, and audio messages in select regions.
When using mobile data
Selected media will automatically download when you are connected to cellular data.
When connected on Wi-Fi
Selected media will automatically download when you are connected to Wi-Fi.
When roaming
Selected media will automatically download when you are roaming.
Note: Enabling auto-download when roaming might result in significantly increased charges from your mobile provider as roaming data is often expensive.
Automatically downloaded media will show up in your gallery. If you want to stop all WhatsApp media from appearing in your gallery, we recommend that you create a .nomedia file or folder inside your WhatsApp images, audio and video folder. You can do this using a file explorer from the Google Play Store. If you change your mind later, you can simply delete the .nomedia file and WhatsApp media will show up in your gallery again.
Related resources:
How to configure auto-download on: iPhone