Yeah, it's definitely fully intentional. Microsoft is known for trying all sorts of tricks to enforce the newest browser and OS versions (with maximized spying tools) on all people, if any possible. So the first thing they did after getting their hands on github was to enforce a newer TLS version, even for simply *reading* public pages. In one scoop kicking out all users of really old browsers knowing max TLS1.0 (perhaps 1.1 too, don't know), and even worse, also making it impossible for them to download anything from github anymore. Countless useful apps developed for OLD browsers now inaccessible, and updates to those, and even Linux builds.
And shortly after people here reported that Microsoft now also blocked access to a few of the advanced github-features for members, by enforcing really latest greatest javascript and the most modern browsers on them, if I got that right.
That fits also perfectly to this discovery that Microsoft-Github now only allows full access for the current Firefox ESR 60 version too, by intentionally using most modern JS code, and even the previous FF-esr is already ignored!
They clearly do this by design. Trying to enforce as much as they can their latest systems and browsers with maximized spying build-in and minimized customizing possibilities for users. Like others too of course (e.g. Mozilla deleting ALL xul-addons which makes no other sense at all, instead of simply keeping a frozen archive, and Opera deleted all Presto-addons long since too)
Regarding really old browsers again, luckily one of them could already handle some TLS1.2 and html5: Opera Presto 12.02. The prob is, that's not widely known, sadly I learned this only last year. And meanwhile, what hardly anyone knows, there's also retrozilla (FF2) and a few old gecko builds with added TLS1.2 by roytam1, working miracles in modern web, even on 98se with kernelex: you wouldn't believe how many sites become at least readable again simply by being allowed access. Without frills and only limited functions of course, but blocking css sometimes works the next miracle, revealing input boxes, text content, many images, making some broken links clickable. BTW also making some too heavy css-overloaded pages scrollable again, fast. For miracle step #3 fiddling with userstyles+scripts often helps (for this forum too) All that stuff doesn't help always, but well enough in most cases.
Point being:
Yes they are fully intentionally trying to kick out users of even slightly older browsers versions, for their own hidden agendas, without real need.