I started making this list for a friend and fellow Christian Universalist, 2nd Timothy Group, but decided it might be useful for others too, so I'm posting it publicly.
Christian Forums.com (Debate forum. The one with the most active Christian Universalists. As well, the user Deafsilence is working on creating weekly meetings on Zoom for all us Christian Universalists to talk in).
Tentmaker.org (Only Christian Universalists talk here)
Christian Universalism Subreddit (Post oriented, with comment sections)
Christianity Board.com (Least active)
Christianity Forums.net (Less active)
City Data Universalism Thread (No separate threads, many Christian Universalists are here too)
Christian Universalism Discord (Have to join as member to see messages).
And as a reminder, please save the links of any good Christian Universalism discussions on the Internet Archive using the Wayback Machine. Or make an offline copy with WinHTTrack Website Copier.
That's all I have currently. Feel free to comment down below any that I missed :)