The cable does not produce noise by itself. It acts as an antenna that can channel outside interference, and then there is just the inherent noise of high frequency electronics. Cat 8 standards are needed to successfully transfer data at high volume, read high frequency, needed for faster networks.
Look inside high end digital equipment and you might see dividers or optical isolators between various boards that are used to prevent noise bleeding into the signal. This is not by accident. And I am quite sure the engineers at Aurender, Innuos and Antipodes could all share their measurements and explain how they have worked to remove noise from the digital chain.How does it affect sound quality? Mitigating noise reduces your noise floor. The importance and effect of this cannot be quantified in words, only by hearing the results.
This is all very true. In very cheap and poorly constructed digital cables, noise rides along and can potentially cause more problems. This is because they are very poorly shielded and act as antennas. The very same thing happens with very cheap digital cables - such as PMMA (plastic) TOSLINK (that are typically free-bees) and random brand RCA digital cables. I always go for glass fiber TOSLINK and robust, triple shielded (if in a noisy room with a router etc.). digital cables.
My Son is a Network Engineer, he used these cables for his exam, and in his home lab: Amazon.com: CAT8 Ethernet Cable, Hagibis 360° LAN Network Cable with Zinc Alloy RJ45, Braided 24AWG 40Gbps 2000Mhz Patch Cord High Speed for Gaming, PS4, Xbox, Modem, Router, PC, Laptop : Electronics
He is a CCIE and has been teaching me about computer networking since he learned it about 8 years ago.
Better to pay for quality if it’s inexpensive anyway. I would avoid no-name brands or extremely cheap ethernet cables, as some may be poorly tested. I always research the brand before I buy. We use these cables extensively in the home.

