hdmi 2.1 has more bandwidth. depends on resolution of your oled, if its 4k it probably doesn't matter. hdmi 2.1 might allow 12-bit color More on reddit.com

As far as i know DisplayPort is better than HDMI More on reddit.com

Short answer: If you don't want to think about the version of the cable, the easy way to go about it is to get a DisplayPort cable. The most common version of DisplayPort cables, 1.4, support higher resolutions and higher refresh rates than the most common version of HDMI. Long answer: The most common version of DisplayPort is DisplayPort 1.4. It's able to transfer up to 32.40 Gbit/s of information. That information is the actual image to your monitor, and how fast it can be sent. More Gbit/s, the higher the resolution and the higher the refresh rate that cable supports. The most common version of HDMI, HDMI 2.0, supports up to 18.00 Gbit/s, almost half of the transfer rate of DisplayPort 1.4. So HDMI 2.0 cables can't support nowhere near as many resolutions and refresh rates than DisplayPort 1.4 cables. But, there is a new update to HDMI called HDMI 2.1 that increases the amount of information being sent to 48.00 Gbit/s, a solid chunk more than DisplayPort 1.4. This allows for really high end monitor resolutions, like 4K, to run at very high refresh rates, like 240 Hz. But HDMI 2.1 has been slow to adopt, not all HDMI cables that say they are 2.1 can actually reach 2.1 speeds, and the organization that manages the HDMI standard recently did some changes that makes it rather hard to see if an HDMI cable that says it is 2.1 can actually reach 48 Gbit/s. See this video to understand the HDMI 2.1 fiasco: https://youtu.be/qU9g9BO3q4w (The last point is the real issue with HDMI 2.1. It's a whole issue that's been ranted on by Linus Tech Tips) More on reddit.com

I've read that there are technical reasons Windows would say 59Hz but it would actually be 60Hz. Does anyone have a clear answer/explanation? Well, technically it's 59.94 Hz, which is double 29.97Hz, which is the NTSC M standard for TV's. There's a good chance that your monitor is actually only 59.94 Hz. More on reddit.com