That is incorrect with regard to groups.io unless something has changed radically.  You are required to establish a password for website access on activation of the link sent.

Now, you can remain logged in under any given browser for a long time after having logged in.  I use the web interface almost exclusively and can't remember the last time I actually had to log in.  My session cookie lasts for months, that's for certain if I don't intentionally log out.
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Brian - Windows 10, 64-Bit, Version 21H2, Build 19044  

You can't crush ideas by suppressing them. You can only crush them by ignoring them.
     ~ Ursula LeGuin, The Dispossessed