There are high speed cables and standard cables (w/ and w/o ethernet). High speed cables are found pretty much everywhere nowadays. HDMI 2.1 *will* require new cables, but that's not what we're talking about right now.
If you have a reliable (keyword) high speed cable, it will be fully compliant with 4K, HDR, HDCP 2.2 etc. (HDCP is contingent on the devices themselves being compliant, not the HDMI cable). I've had cheap $1 cables that worked perfectly, while another would be unstable. Luck of the draw I suppose when dealing with cheap cables not being up to claimed specs, but let's not throw around misinformation.
Please stop perpetuating this "NEED HDMI 2.0 cable" nonsense.
The point is, test out your existing cables and see if you're getting the appropriate 4K and HDR being handled BEFORE running out and buying one. Make sure every device in your chain is HDCP 2.2 compliant. Incompatibility/instability should crop up instantly. If they aren't up to spec, then try it with another one you have lying around. And if those don't work, go ahead and grab a new shiny advertised "4K HDR HDMI 2.0" cable.
...or just stop wasting time with these free or super cheap cables, spend an extra couple bucks and get a premium certified cable from someplace like monoprice.