Sure. It's using OS networking APIs. Or running in a virtual machine.
> Would you consider it secure enough to open your banking website on it?
If I'm running 20 year old software, it's probably to interact with a legacy system. There are still businesses that run on like 486's with Windows 3.1. This is more common than you think!
> The bar is whether the machine is usable (secure).
The bar is whatever I WANT it to be, it's my machine, and it's pretentious of a software developer to assume they know what I'm using the software for and what my best interests are. For all they know I'm using the software in a museum, 20 years from now, about this era of computing.