Android notification large icon specification?

Where can I find the correct size of a large icon for Android notifications?

What do I want? I want a nice looking circle (some color) as a big icon with a big surround. And add a small icon with its own specifications

The small icon works normally. But I have questions about the large icon. I searched for hours, but I couldn't find it!

What space can large icons use? How big is the space? How big should the small envelope in the "big" icon be?

Android KitKat and later:

Large icon (space I can fill): large icon (how big must the small envelope be? What are the specifications?):

Under Android KitKat:

I know that the notification is somewhat different under Android KitKat. But what are the specifications here?

Large icon (space I can fill): large icon (how big must the small envelope be? What are the specifications?):

The question of large notification icon background is a bit like this one. However, this question did not get the final answer. The accepted answer did not convince me because there was discussion and no conclusion in the comments

resolvent:

The large icon of xxhdpi must be 256 × 256 pixels

Get Android notification icons from onesignal document