macOS web browsers have shown their OS as a variation of "Intel Mac OS X 10.15" since 2014's 10.15 Yosemite. These user agent string are from my M4 Mac running the latest Tahoe macOS:

Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:152.0) Gecko/20100101 Firefox/152.0
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/150.0.0.0 Safari/537.36

Yep. Struggling to see the difference between this and the 2600+ beyond the wireless controller support. Stella in a less iconic box. The wireless CX40s apparently work with original '70s 2600s. That's pretty cool.

Something like polyglot markup? http://dev.w3.org/html5/html-xhtml-author-guide/html-xhtml-authoring-guide.html This relies on the fact that XHTML markup is actually valid in HTML5. It may have taken them seven years to catch up with you, but they're there now. ;)