Matter is a communication protocol built on top of TCP/IP networking designed to provide interoperability between different home automation ecosystems. Matter can run over a Thread wireless mesh network (typically for low powered devices) or over Wi-Fi (typically for mains powered devices). In both cases, Matter runs on top of IPv6 network addressing.
Whether a hub is required depends on a couple of different things. First, since Thread is a wireless protocol that runs over the 2.4Ghz radio spectrum, you need some device that provides that capability. For ST, that’s either a v2/v3/Aeotec hub, the ST Station hub, or a Samsung TV or fridge with the Zigbee/Thread dongle. Other manufacturers may provide Zigbee/Thread radios in their devices, for instance, some Amazon Echo devices support Matter over Thread.
Second, regardless of the transport medium, Thread or Wi-fi, you need a Matter controller, something that can manage a set of Matter devices. For ST, that’s the same set of devices that I mentioned above plus the ST Wi-fi Hubs. WRT to other manufacturers, my experience has been that you still need some hardware device to be the central manager and controller, though that need not be a dedicated “hub” but rather something like an Amazon Echo Show, Dot, etc., an Apple TV 4K, or a newer model Samsung TV. For instance, I have Leviton Matter over Wi-Fi switches and dimmers at one of my houses that were commissioned using the Alexa app with the controller being an Echo Dot 4 (I use ST at the same location but only for cloud->cloud integrated Wi-Fi devices).
So, long story short, no you don’t necessarily need a dedicated hub. But, you do need something to be the controller for Matter devices and that, at this point in time, is some hardware device. To learn more about Matter, here is a topic that discusses it in some detail. I’d look at the more recent discussions since it goes back to the original beginning of Matter. Also, this is a good synopsis of all the Matter capable devices as of 2023.