Can't add some Widgets to "my Apps"

[mito]

Hi there,
it's my first post here and I like to say "Hallo" to everyone.
I have a problem with the "my Apps" section in the smart Hub. In german it is the "Eigene Apps"-section. So let's take a look at the screenshot. I have several apps installed (for example "Tagesschau" or "Putpat TV") and they are running fine. But I can't add them to "my Apps" because they are not listed on the screen for editing this section. Can anybody help?
Thanks.

PS: The TV came with some apps preinstalled (Fitness and Kids), but I can't uninstall them. How can I get rid of it?