Need to first make sure your monitor/TV has HDMI 2.1, also. And that your cable is an HDMI 2.1 cable. But, that's going to come only on 8k monitors and TV's. So there is no reason to buy an HDMI 2.1 cable unless you have one of those monitors.
Another thing the typical person never looks into is the quality of your HDMI cable. People think all HDMI 2.0 cables are the same and can give the same bandwidth. Not true at all. I've looked into this and it's so rampant how many cables out there (HDMI cable for $1.99 anyone?) that actually do not give you the correct bandwidth or their quality degrades so rapidly over time that the bandwidth decreases as well and you end up not getting the supposed resolution you think you are getting.
Also, for those with monitors that use HDMI 2.0 or Displayport 1.4a I would heavily suggest going with a displayport cable since it has almost double the bandwidth. But if you have an HDMI 2.1 machine AND HDMI 2.1 monitor then use HDMI 2.1 as it has a larger bandwidth...until Displayport 2.0 comes out on monitors which will again crush HDMI 2.1. Here is a good article to read that also has a table giving the bandwidth on both connections. As you can see, displayport is far superior to HDMI if you can use it. Just make sure your cord is NOT CHEAP!!! Very important to know this as all HDMI 2.0 cables, or HDMI 2.1 cables , or Displayport 1.4a cables, etc. are not created equal. Spend the extra bucks to buy a good cable.
DisplayPort vs. HDMI: Which Is Better For Gaming? | Tom's Hardware
After reading this article you can see how a 4k monitor with a 144hz refresh rate will actually not get you that 144hz refresh rate with an HDMI 2.0 cable. You need a Displayport 1.4/1.4a cable in order to achieve that as it has the bandwidth support to allow it.
For reference, I personally use the AudioQuest line for my HDMI cables. You can find them at Best Buy.