The original 6D was called the "best low light camera" in its day. Other cameras have since been introduced that are better, but at the time the 6D was king. Part of the reason for it's excellent high ISO performance was it's "uncrowded" full frame sensor... a very modest 20MP in a large sensor. Many people think the newer 6D Mark II has about the same high ISO performance, though it's got 30% higher resolution (26MP).
It's the only Canon model to ever use an 11-point AF system (there were earlier models with 9-point and 7-point, concurrent models with 19-point and 61-point, as well as later 45-point and 65-point Canon DSLR AF systems... but no other Canon DSLR with 11-point AF). The center point of the 6D's AF array is high performance "dual axis/cross type" which can focus in as low as -3EV light levels (approx. "moonlight"). This combines well with the 6D's high ISO capability. Unfortunately, the other ten AF points are lower performance "single axis" type that are nowhere near as high performance... limited to about -1EV light levels, slower and more likely to hunt. (Compare to 5D Mark IV with 61-point AF, 41 of which are "cross type". Or to 7D Mark II with 65-point AF, all of which are cross type.
It's an "entry level" full frame model, using a lower specification shutter... 1/4000 top speed and 1/180 flash sync (compared to 1/8000 and 1/200 on 5D-series). I don't know if Canon ever officially rated the shutter for durability, but would be surprised if it were more than 100,000 "clicks" (compare to 150,000 or 200,000 on 5D-series and 7D-series). It's also got a single SD memory card slot, minimal sealing for weather/dust resistance, and a fairly slow 4.5 frame per second continuous shooting rate (compare to 5DIV with dual memory card slots, better sealing and 7 fps shooting rate... or similar upgrades in 7DII with 10 fps shooting).
6D is not an ideal "sports/action" camera. But it's quite capable for a lot of things.
High ISO comparison of 6D and 6D II:
https://petapixel.com/2018/02/21/canon-6d-vs-6d-mark-ii-real-life-noise-comparison/Spec comparisons...
6D versus 6D II:
https://cameradecision.com/compare/Canon-EOS-6D-vs-Canon-EOS-6D-Mark-II6D versus 5D Mark III (older):
https://cameradecision.com/compare/Canon-EOS-6D-vs-Canon-EOS-5D-Mark-III6D versus 5D Mark IV (newer):
https://cameradecision.com/compare/Canon-EOS-6D-vs-Canon-EOS-5D-Mark-IV6D versus EOS RP mirrorless:
https://cameradecision.com/compare/Canon-EOS-6D-vs-Canon-EOS-RP6D versus Nikon D610:
https://cameradecision.com/compare/Canon-EOS-6D-vs-Nikon-D6106D versus Nikon D750:
https://cameradecision.com/compare/Canon-EOS-6D-vs-Nikon-D750Lens...
If I were choosing a "standard/walkaround" lens for use on 6D, I'd pick the EF 24-70mm f/4L IS USM... It's a great lens with exceptionally high magnification (probably wouldn't need a separate macro lens). It's also smaller, lighter and less expensive than the EF 24-70mm f/2.8L that I already have. 6D more commonly came with either the EF 24-105L IS (1st version) or the less expensive EF 24-105mm f/3.5-4.5 IS STM, neither of which do much for me.
For landscapes, I'd add an EF 16-35mm f/4L IS USM (also smaller, lighter and less expensive than the f/2.8 version).
And I've already got an EF 100-400mm IS USM "II" that I'd probably use with it at times for sports or wildlife (unfortunately, can't combine with a 1.4X teleconverter on 6D... no autofocus... 6DII or 5DIII or IV can focus that combo).
For low light, portraits, maybe street photography, I'd use EF 28mm f/1.8 USM and/or 35mm f/2 IS USM... and maybe 85mm f/1.8 USM.