USB4 is essentially Thunderbolt 3. Since TB3 also defines how a USB 1-3 connection can be pushed over the wire, that's what most devices can fall back to.
So you are telling me a usb microphone needs to implement hdmi and displayport if it wants to be compliant? Or are these devices expected to stay on lower usb versions? What if the device needs some of the features from usb4 but it makes no sense to have thunderbolt features?
> So you are telling me a usb microphone needs to implement hdmi and displayport if it wants to be compliant? Or are these devices expected to stay on lower usb versions? What if the device needs some of the features from usb4 but it makes no sense to have thunderbolt features?
All USB Type-C connectors all have a pair of USB 2.0 wires in them. You can still be a USB 2.0 device and talk on those USB 2.0 pairs on USB3 (and presumably USB4) just fine with just a little bit of care (get your resistors correct on the CC lines, for example).
If you want some features of USB3 or USB4, then things get a little more complicated. For example, if you want to be able to draw slightly higher power (900mA or 1.5A), then you need to have some active circuitry on the CC lines (One of these is about 70 cents: https://www.ti.com/product/TUSB320HAI) and you have to respond properly when the system tells you to draw less power even though you don't need to use the full-blown USB3 communication pairs.
If, however, you want USB3 or USB4 speed or very high power, then you need a full-blown controller chip and you incur all the grief that demands. Of course, if you actually need a couple Gbps, you're in the realm of doing serious signal integrity analysis anyway, and you're probably not going to balk at the $3-$5 required for a true controller chip to handle it all.
The only new feature in USB4 is Thunderbolt, so yes, if a device doesn't need Thunderbolt features it should stay on an older version. Of course, older USB versions will end up rebranded as something like "USB 4.0 1x1 High Speed".