@Gold, Petr Thanks for posting in our Q&A. From your description, did you mean that you want to add Remote Desktop app as a single app in this kiosk device and access the internal application in the server "X“ via Remote Desktop app? If there is any misunderstanding, please correct me.
Did you set kisok mode via intune? If yes, it is suggested to try to deploy Remote Desktop as a store app via intune and add Remote Desktop in kiosk profile.
https://learn.microsoft.com/en-us/mem/intune/configuration/kiosk-settings-windows#single-app-full-screen-kiosk
Then if you have some specific configurations about Remote Desktop, please deploy configuration profiles or scripts to it.
Hope it will give you some ideas.
If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.