(And apologies for the off-topic post)
Your message fails DKIM and DMARC, probably because it's passing through the mailing list, and DMARC/DKIM broke mailing lists rather badly. (There's a vast amount of politics and big business behind this breakage, and I am willing to rant for literally hours over it, but perhaps for another time).
The solution seems to be to ensure the mailing list system detects DKIM/DMARC and, if needed, change the sender. If this sounds like an awful hack to you, you'd be right, but it seems to be all we have. I understand the mailing lists might be moving to a different provider soon, so perhaps this gets fixed by the change?
You could also change your DKIM/DMARC stuff to only soft-fail, I believe, since it's currently a hard fail and this would explain why some mail providers drop the message entirely, rather than "only" redirecting it to Spam.
I do respect you for trying to self-host email, despite how insanely hard that's becoming. I'm supposedly meant to know about these things, and I gave up some time ago.
Dave.