Status bar on Android P shows only four notification icons
If more than four notifications have been received, the four icons will be followed by a string of dots. Each dot represents another notification received, although it doesn't show which app received it. You will have to pull down the notifications shade to see which apps sent you all of the notifications you have received. As a comparison, on Android Oreo, there is room in the status bar to show as many as seven notification icons.
Android P will be released later this year, and it is unclear whether the limit of four notification icons on un-notched models is being done for the developer preview only, so that developers can get an idea about what the status bar will look like on notched handsets.
An example of what the status bar on Android P looks like can be seen on the image that accompanies this story. Also, note the new home button at the bottom of the screen. The multitask button is gone, replaced by a gesture, and the back button only appears in situations when it can be used. Since the picture shows the home screen, the back button is disabled.