Normally, Internet > Modem > Firewall > Router / Switch > Lan > VIrtual Lan
VLan1 - admin (denied access to every one) inc internet
Vlan 2 - trusted applications face internet
Vlan 3 - TVs and speakers need access to internet
Vlan 4 - Untrusted devices inc IOTs - denied internet access
Vlan 5 - can be critical apps are isolated and allowed internet access. You can have your NAS here or spin off a seperate LAN. Nas will be denied internet access. All Nas patches are done locally.
Vlan 5 can have access to NAS and the same for Vlan 3. But, Vlan3 can only read.
Unless the rules are enabled to deny internet access on the router, anything connected to the modem will get access.
I don’t have the need for Nas as I don’t store music, movies, etc. All are subscriptions. My music - whatever we have - backed up by one drive under family plan. I have a local back up should anything happen.
Judging at the firewall rules, the NAS has access to the net!
I haven’t used QNAP or Synology and hence the advise to go to the SNB!