Firstly thank you for your interest in our product, much appreciated!
Let me explain a bit how spacedesk Viewer works, and what you can do with it.
The spacedesk UWP application, after you connected, has two distinct modes of operation:
1. the View mode, in which you, as the user, are passive, meaning you can't interract with the server connected to (E.g. watching a movie etc)
2. the Remote Control mode, in which you can actively operate the server through available user input devices from your client machine.
Right after you connect to the server, the application goes into View mode. Here, apart from watching the server's screen, you can interact with the view (panning the screen view, rotating on different axis and zooming).
You can also access the command bar at the top of the viewer, by taping with one finger (or moving the mouse/pen cursor to the top of the viewer). Another touchscreen tap and you hide the menu again. Please note, that Pen has to be enabled first (either by settings or from this command bar (the button with the pen icon).
This is all here really - and you, on problem described at 1. and 2., were only dragging and rotating the screen view either by touch (1 finger drag) and by pen drag.
You definitely want to get into the Remote Control mode, to operate the server from your client (tablet).
To enter the Remote Control mode, depending on your input, you have to:
a. tap with 3 fingers the screen, for touchscreen input
b. tap with your pen (bring the tip in contact with the surface and back), for pen
c. tap with the mouse/trackpad (mouse click), for mouse
After you confirm the dialog box, you are in Remote Control. You can exit any time the Remote Control with the same gesture like above.
I hope these explanation clarified a bit how and what you can do with spacedesk Viewer.