If you type ‘-previous’ after the ‘docs’ word on the URL then 9 times out of 10 you’ll be able to find the documentation for the older releases.
The new Platform Support Guide is not uploaded yet. It will be posted to the new Pega Documentation site here. NOTE: Due to the changeover in Documentation sites, some links in the Guide may not work for a day or two.
I will update this post once I hear more from the documentation team.