First off: cables don't have version numbers. The host and the client have ports that adhere to a certain spec and the HDMI foundation made that very unclear by incorporating 2.0b into 2.1 and now not every 2.1 port supports the same things. Cables are defined by their max bandwidth, i.e. high speed, ultra high speed or high speed with ethernet. You might see marketers saying something is a 2.1 cable, that just means it is capable of supporting some or all of the 2.1 spec.
Second: the only reason to get new HDMI cables, like you said, is if you currently have a very old one and have devices that actually make use of the bandwidth. And I'll tell you right now, most of the high speed cables will do just fine. It's when you start doing 8k120 with HDR and VRR with eARC you'll need heftier cables. The only external devices to support that, though, are either supplied with cables because their makers don't want you bottlenecking your device, or they are PCs.
Third: the only reason HDMI is even a thing is because this joint venture behind it successfully lobbied their inferior product to TV manufacturers. DisplayPort has always been and will always be the better interface for video.