Why is certain apps not compatible with iPhone

You're talking about a third-party app here, developed by Kraus und Karnth (if I found the right app in the App Store). Not by Apple. While Apple provides the underlying technology for all apps on the phone it's up to the developers to make good programs with it.

Streaming apps are dependent on a lot of things to get images flowing to your screen:

• the quality of the signal where you are located, cellular or wifi
• the characteristics of the video feed (size, resolution, frames per second, etc.)
• the bandwidth of the content servers

Pus since Apple released a new iOS version with new or modified programming interfaces for the apps, the developers of any program may take some time to get used to them and iron out all the bugs in their app.

Contact the developers and explain your difficulties and their circumstances, you may be helping them improve their product.

If you want any kind of assistance you have to provide specific details.

• What is your phone model?
• What version of iOS does it run?
• What are the apps you're talking about?
• What are they not doing that you think they should do?
• In what circumstances are they not responding?
• Have you tried any troubleshooting, like doing some actions differently?