@Otto Pylot -
High Speed HDMI is not a 'non-certified' cable. Any cable can make any claim, but to carry logos from hdmi.org they all must be certified to meet the speed/resolution requirements for each class. So, to say your cable is capable of 48Gb/s bandwidth (HDMI 2.1 full resolution), they can do so. But, to carry the HDMI Ultra High Speed logo, then it must be certified at that speed. The same is true for all versions of HDMI cables that carry an official logo.
HDMI has a full writeup of their different cable types and classifications right here:
HDMI cable overview with the different HDMI cable types, their port capabilities, and how to tell the HDMI connector types apart. HDMI 2.1b
hdmi.org
I typically refer to them in bandwidth categories. Most cables you buy are 10Gb/s capable. That's enough for 1080p viewing. It was the first generation of 4K at 30Hz, but not enough for all the new 4K displays on the market which need an 18Gb/s connection.
As to actual cable differences, I would expect that most of it is similar to how cat5e, cat6, cat7, etc. are different. They build the cables to a higher tolerance rating. They use more twists, better shielding, and newer technology to build the cables to pass the bandwidth that is required. The jump from 720p to 1080p wasn't a huge issue, but there were some cables which couldn't handle 1080p/60 years ago. But, the jump from the 4Gb/s which 1080p requires to the 18Gb/s which 4K/60 requires has been crushing to many cables and the components which connect them.
To this day, there is not a wall plate which you can plug in a 4K source and reliably pass it up to a TV easily. No standard keystone HDMI connections can do it. I have yet to see an active wall plate which can do it which isn't $1,000+.
8K and 48Gb/s (HDMI 2.1) is another level. There are cables coming to market which make claims for 48Gb/s support. But, anything claiming HDMI 2.1 support is something to be wary of. The full 48Gb/s bandwidth is rarely supported in any new product. Most just support some lower level of bandwidth. 33Gb/s or so. The PS5 and XBox Series are excellent examples of products which go beyond HDMI 2.0, but aren't full bandwidth HDMI 2.1.
All of this, and HDMI still doesn't require a stereo stream alongside surround sound in all of their products so you can hook up headphones or a second zone easily.