I have stumbled across some information that has been described in various Advanced User Guides as being available on the Canon USA website, but it wasn’t clear where to find it. At least it wasn’t clear to me. As it turns out, the link to the information seems to be in every Advanced User Guide.
https://cam.start.canon/en/H001/
As my grandfather would say, “If it were a snake, it would have bit ya.”
The cam.start.canon website is run by Canon Inc. in Japan. Canon Inc. also supplies information to the other regions such as Canon USA, Canon Japan, Canon Europe etc who publish on their own websites. However the instruction guides created by Canon Inc all reference the cam.start.canon website. From that you can find the latest manuals in PDF and HTML formats for most current cameras. Most of the individual camera pages also have the link to the supplemental information page you mention above.
As an example here's the EOS R6 Mark II page, and you'll see in the lower left corner is the supplemental information button.
