You have actually enrolled your device into Work Profile mode using an Android Enterprise device agent, and not an OEM specific Android-Plus device agent.  In fact, I check Soti agent download page and  there doesn't seem to have any Android plus device agent for  Gigaset GX290.

As your device is using Android-Enterprise device agent, any Google Play app added in any app catalog rule will not be visible as expected.  You have to create an MG or MGP account, update your add-devices rule, re-enrol your device to be assoicated with the added account, and modify your app-catalog rule to use managed Google-Play store instead.

Android Enterprise Work Profile mode is meant for BYOD  (containerization) use case.  If you intend to have full control of the device, you should enrol it into AE Managed-Device (or Device-Owner) mode, which requires factory reset of your device.   Check the onlline manual and other thread on this forum on various approaches to enrol into this MD/DO mode.

Also, make sure you have the Gigaset AE plug-in  updated on your server and the corresponding .pcg package is deployed to your device for some advanced features (e.g. full remote control)  to work.

I only have experience with Managed Play & App Catalog with Android Enterprise devices so I'm not entirely sure what is possible under Android+ but I would have to imagine it would be limited. When you enroll a device with Android Enterprise SOTI can help assign a randomized account on the device so that it can download applications through Managed Play. With Device Admin (Android+) based management I feel like you'd struggle with the account piece. 

You have to check-in devices so apps are shown in catalog

Hello,

thanks for your answers.

To be more precise: I have not set up an Android Enterprise binding. I added 'Google Play Store applications' and NOT 'Managed Google Play applications'

I've just performed a test on an MobiConrol v15.0.1.1181 cloud server using a Samsung device, and app-catalog rule works fine.

What is the brand and model of your device?

What are version and build numbers of your device agent?

What are the active MDM API's reported by your device agent?

Have you successfully deployed any profiles to the device?   

What is the brand and model of your device? Gigaset, GX290

What are version and build numbers of your device agent? 14.1.4 Build 1010

What are the active MDM API's reported by your device agent? Work Profile, Remote View (1.16.10.121)

Have you successfully deployed any profiles to the device? No

Thank you for clarification.