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I wouldn't do a mailing list these days, but as someone who spent the early part of my career interacting with devs that preferred this method, it's actually pretty ergonomic by a 2005 standard. A message thread aware, text based email client that can turn messages into patches in a keystroke makes it actually pretty comparable to modern code review...
I think it's hard for younger devs to get this because they're used to email being stuck in a crappy, unthreaded browser interface or Outlook etc. (which are terrible for mailing lists) and most collaboration taking place in code review and chat platforms like Teams/Slack but for decades before these were feasible, email was the way...
It certainly beats Teams, Slack, or Discord. For a start, you have control over the messages and can actually search on them.
Matrix?
I'll note that a number of groups and forums send mailing list like emails (google groups, django dev being a big one) and that notifications can be threaded from places like Github with the right client.
Thunderbird has good threading.
Roundcube webmail is also capable here. Though when I have had it working it didn't include sent messages... which is not great in my mind.