Hi Marco,
I reply in English so that everyone can understand the post - I hope that's OK with you.
Adding status overlay icons is a nice suggestion. We'll think about it even though it probably won't be implemented in the short term except there's a code contribution or sponsored development. At least the current active feature(s) is always displayed in the tooltip of a computer so if unsure either look at the tooltip or simply click the "Overview" button in the toolbar (again) which will always stop any active features on all computers.
The same applies for locking input devices only without blaking the screen. We hope to have this in Veyon 5.
Running the demo mode on computers which no users are logged on is not possible and technically very difficult so it's very unlikely to find a solution here.
Best regards
Tobias