WhatsApp gets a new function to display low priority notifications. If this option is activated, notifications will no longer appear as 'heads up' notification at the top of the screen. Instead, the notifications appear only as an icon in the notification bar.
The new option is found in the latest beta (version 2.18.117) of WhatsApp. In the beta, you can indicate whether the notifications of WhatsApp have priority or not. Notifications with priority are at the top, even if there are newer notifications. The function only works from Android 5.0 and higher, because Google introduced heads-up notifications. From Android 8.0 you can also use Notification Channels to adjust the priority of notifications for group chat and private chat, for example.
WhatsApp is currently providing high priority notifications, but soon you will be able to indicate the low priority notifications. It is not possible to set the notification priority per chat or contact person. However, you can enable high priority notifications for a private chat and stake out for group chat.