Vpn says "network secure" and nothing on this galaxy will enable VPN.
I don't think Norton can say if the entire internet is safe but they certainly won't allow their clients to determine whether they want vpn on or not. Why do they sell it but not let their customers use it?
What device and Android version are you using?
If you are at home with a properly secured router, your network is secure. So you do not need a VPN for security purposes. Here is a Norton Blog on this. https://us.norton.com/blog/privacy/do-you-need-a-vpn-at-home
The VPN would be needed when using a public hotspot that does not require a password to access.
Having said that, you should be able to turn on the VPN manually if you choose. I can confirm that my Samsung Tab A on Android 9 is not allowing manual use of the VPN feature on my home secured network. I'll send logs for this and it would help if you could also send logs.
Open the 360 app and tap the three bars at the top left. Tap on Settings > General, and scroll down to the Logging section. Turn on Enable Debug Log. Then continue using your device until your issue happens again. In this case have your tablet connected to your network and try a few times to turn on the VPN feature. After the issue has happened, go back to the Debug Log settings and then tap on Send Error Report with log files. In your submission please include "forum 'your username' " in the Case ID section of the report. Also include a link to this thread. You can turn off logging when you have sent the logs.
If you do send logs, please let me know and I'll notify my contacts to look for them.