Add suspend my input to Default Session Settings
Would be super helpful to be able to have suspend my input switched on by default so if you join an existing session you don't accidentally start clicking and moving things around on someone's screen. You should then still have the ability to switch this off once you do need to actually control something on the screen just like you can with other 5 options in Default Session settings screen.
Looks like there is another way - try this.
Admin > Advanced > Other settings (Application Configuration). Find and tick the options for Suspend Host Control
The wording says
"Prevent the host from controlling the guest's keyboard and mouse upon initial connection."
If you don't see the Advanced menu you need to install a extension called 'Advanced Configuration Editor' by 'ConnectWise Labs'