Not sure what kind of traffic you mean? There are many applications working as servers that do that. Also operating system itself does that between computers in the same network - that's how internal naming system works (without a DNS server). Now that you are running Wireshark, that causes network traffic by itself.
If you do not want that to happen by default, you would need have your two VMs in separate networks - now they are in the same NAT network. You could create another network, but easiest way is probably in Workstation Pro (install it and network configuration GUI is still available after evaluation time expires). You could also put the other one in Host-only network but then you would still have some traffic between Host and VM.
Those wouldn't still prevent Wireshark causing network traffic, but that is most likely to be able to scan different networks - depending on how you run it.
So, if you have minimum traffic - that is how OS's work or that is what you cause with Wireshark.
If you have heavy traffic - you either have installed servers that you are not aware of or you have some other type of unknown software running in your system - cannot speculate on what that unknown might be. Typically, nowadays, in corporate PCs all kinds of software is working in the background without the end user knowing about them - that is the point of them. If you got the VM from somewhere else, you might want to install Ubuntu with its defaults and see how that behaves - it only takes 1-2 hours to get Ubuntu running in VM (depends on Internet speed, however). Just as an example: If you have Microsoft Teams installed, it spies on what you do and sends a report to your boss ... that is bound to cause some network traffic - not exactly sure what Debian version of Teams is doing.
