You hit a physical button and an internal kvm switches usb input and displayport out between primary and secondary machine. There is no shared clipboard or way for data to be intentionally be shared between machines and nothing to distinguish this setup from any other "secure" setup to disallow its use. It ticks the correct boxes to meet the described intent of the feature and unlike a secure environment one is obliged to use for everything would actually be more secure as you have no good reason to install a bunch of software or browse random websites on the slower secure environment.
I don't think you'll need to buy an SBC for this. A weekend of messing with virtual machines will be enough.
https://stackoverflow.com/questions/39533/how-to-identify-th...
I don't think big websites will block every VM (especially since Microsoft has some kind of super secure browser implementation that uses virtualisation). You may need to make KVM fake HyperV, though.