Then in the desktop version of Thunderbird , "Add a newsgroup account" with your login details from eternal september.
Find some groups to subscribe to. Try comp.lang.python for example. Once you subscribe you can see the posts inside it.
You'll probably see lots of spam. To remove the spam you need to use Thunderbirds Message Filters functionality - remove all messages where their Message-ID header contains "googlegroups".
Someone made the calculation that the data harvested for advertisers is more valuable than the hosting/maintenance expense they would recoup by killing it. Plus it's tasty food for Bard.