[how to turn on developer mode in vive focus 3 ?]

I second this, nothing worse then getting ready to do a demo for potential clients and having to set up the boundary AGAIN after its been set up multiple times.

 

[how to turn off boundary system in vive focus 3]

Yes the boundary is constantly being lost when you take the focus 3 off. Especially for a business demo, you should be able to turn the boundary off.