Due to recent Steam VR v1.9.15 change in the VR launcher, VR user will encounter cannot use exit game/call service when press system button on the controller.
The long-term solution for fixing this issue is released in VIVEPORT Arcade Manager Client version 3.0.2.26 [updated 2020/01/09], please check your client version and update accordingly via SETTINGS>>VERSION on VAM host.
If you do not want to update your client version, you can refer to below workaround before the fix:
Step 1
When the launcher is up, click the System button on the controller
Step 2
Click VIVEPORT button (highlighted red)
Step 3
Enter Game, click System button again, and you will be able to launch Arcade Dashboard now