Nat ok, but no bridge adapter and connection problems

[science2002]

I'm still using VB v. 6.1 with Win10 LTSC as a guest on Win10 Pro as a host.
I shall attempt to put my question in a more general form, although my problem is rather specific.

1. Premise: NAT is the only network that works on my guest OS. I tried, but the Bridge adapter connected to my portable's Intel Wi-Fi 6 card does not work. The same outcome is with the other VB network's options.
2. I installed a software (WebEx by Cisco) that uses - I guess - a few no-standard protocols and ports for its digital phone service.
3. After the first connection, the Firewall detected the need for the app to access with few exe the internet (the NAT) and asked permission.
4. However, the digital phone does not work with audio in (always) and out (except in one specific scenario of internal numbers). Better, it only works if I use my institution's VPN (Global Access as its app.), which is also installed only on the guest OS. However WebEx should work without VPN.

Question:
Can the host OS be the culprit? I mean, could the particular protocols and ports I gave access in the guest machine be blocked by the host machine (for insance by the host firewall)? Did I understand correctly that with NAT the guest internet connection passes through the host internet connection? Can the latter block what is allow in the former?

Thanks.

[BillG]

The NAT setting in VirtualBox works just like any other NAT (Network Address Translation) system. It allows the guest to share the host's Internet connection. The guest vm will have the same restrictions as the host PC.

A bridged connection allows the vm access to one of the host's physical adapters, so any restrictions that the host OS applies to that physical adapter will also affect the vm bridged to it.

[science2002]

Thanks @BillG.
What it is still not clear is the following.
If in the guest OS an app asks to allow to pass by the guest firewall, could it be blocked downstream by the host firewall (where the app is absent) using NAT as VB network connection? Or is it true the opposite (the guest app will access internet without any check by the host firewall)?

[BillG]

In theory, no. The re-routing of the traffic should not be affected by the firewall settings of the device doing the rerouting.

In practice you would have to test each case yourself. It would depend on how intrusive the firewall was. I would not expect the Windows firewall to do that.