Peek notifications on BlackBerry KEYone with Android 7.1.1

Sooo, I finally moved from BlackBerry 10 to the infamous BlackBerry KEYone. Thus far, really liking it overall. Do need to get used to Android as it is my first ever Android device but sure it will work out. Some stuff seems less customisable than BlackBerry 10 but that's unfortunately history now.

I do have a question regarding peek notifications though. BBM for Android has an option for this called "preview" and shows the peek notification when there is an incoming BBM message and the screen is on and you are working in another app. However, this doesn't seem to be working for other communicating apps, like both WhatsApp and Signal. WhatsApp has pop-up notifications, which I don't want, while Signal makes no mention of it at all. Is this because those apps need to implement peek notifications specifically, as it has been changed in 7.1.1? On older Android versions, some type of peek notification is working for those apps, albeit in a less advanced manner.

I would like to know whether that hypothesis is correct or whether I am missing something...

Would like to hear your experiences!

Well, I guess not that many people experience this problem. Googling it I saw that it was more the other way around, people wanting to disable peek notifications!

Finally fixed my problem by using the Power Notification Controls from the System UI Tuner. Set the level for WhatsApp and Signal at four, to always show peek. I am still puzzled why they were disabled in the first place...