There is no such thing as an HDMI 2.0 cable.

There are 4 main types

Standard, and standard with Ethernet – up to 1080i and 720p

High speed, and high speed with Ethernet – 1080p, 4K, 3D, HDR

The "with Ethernet" portion is irrelevant because literally no consumer device uses it.

There is also a new "Premium" certification, but that's just more rigorous testing for high speed cables.

98% of the cables available for sale or that come bundled with devices are high speed cable types, and that's all you need. They will say "high speed" on the jacket of the cable.

Yes it works fine

It needs to be an HDMI cable capable of 18Gbps.

Some older cheaper cables will only be 10Gbps.

I’m willing to bet that the cable that comes with the Mi Box will probably be fine. If it isn’t for some reason, there are plenty of affordable cables that will be: Monoprice, Amazon Basics, etc.