Admob / App open no preview in test mode

This time I wanted to try out the Admob function “app open”. After some tests I can say it doesn’t work. The otherwise proven reward videos, interstitial… work as usual.
They are simply not displayed.
I have built a test into my instructions. See the screenshot.
There are actually only two options. The first display when “app open” does not work in test mode. Or the “show” command is incorrect.
Has anyone noticed anything similar?