You asked

Is the canon eos 6d mark ii good in low light?

The 6D Mark II is a full frame camera, so it has the sensor size that helps most in dim light. Full frame gathers roughly a stop more light than APS-C at the same framing and f-number, so what a bigger sensor buys you applies here. I don't have test results for its high-ISO noise, so I can't give you a number. The body also has no in-body stabilisation, so low light means slow shutter speeds, and you'll want stabilised or fast lenses. For dim rooms and events, I'd look at:

The full catalogue page lists everything that fits it.

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