Any data on Big Sur market share?
In my experience data for macOS adoption (as opposed to iOS) is fraught with inconsistencies. Many sources just lump the different versions of macOS together in the one bucket. Others even lump macOS and iOS together in the same bucket. In some cases, the data is based on web traffic which is also fraught with difficulty (as the same version of browser can be installed on multiple versions of macOS).
One thing to keep in mind is the sale of new Mac hardware will include the latest version of macOS (e.g. the M1 Macs all come with macOS Big Sur pre-installed, etc).
The last figure1 I recall seeing of new Mac sales was  for the three month period ended 26 December 2020 (8,675,000 Macs, a big jump attributed mainly to M1 Macs). However, many new Mac sales occurred prior to the release of macOS Big Sur or the release of M1 Macs, so that figure will be a mixture of macOS Catalina and macOS Big Sur.
However, the reason I mention Mac sales figures is because your post asks at the end about macOS Big Sur having &quot;at least 1k Mac users a month&quot; - which of course is well and truly below the millions it will be based on those sales figures.
In any case, over time sites like statcounter (which you've already referenced) and statista will include the latest version of macOS in their charts etc. And for most people, that is all they can really wait for or rely on in terms of these figures.
1 Condensed Consolidated Statements of Operations, Apple, 27 January 2021.