To be clear, this is the same organization that developed Zigbee, which requires paid certification - without, you're not allowed to say the product supports Zigbee or to use the Zigbee logo.
You can connect devices without this, it just shows a warning during commissioning that the device is not certified. No impact whatsoever.
So by analogy, Zigbee is like USB in that it encourages certification through trademarks, while Matter is like HDCP or Blu-ray in that it enforces certification through technical means (cryptographic signatures)?
You can connect devices without this, it just shows a warning during commissioning that the device is not certified. No impact whatsoever.