The sites are different.
The first is an email mailing list purely for proposing new ideas for the Python language. It is archived at mail.python.org.
The second is a web forum (Discourse) hosted at discuss.python.org. It is organised around many different categories. New ideas is only one category out of many.
The second also sends out messages by email, but support for email is very poor.
There are more people on the Python-Ideas mailing list, but they tend to be much more negative towards new ideas.
The Discourse web forum is younger and newer, with a different set of participants.
You can tell that the sites are different, not just from the completely different URLs and the completely different look, and that you needed different log-ins for them, but also because messages you post to one do not show up on the other.
@steven.daprano thank you for feedback