When sending pgp signed mail the resulted signature ends being broken. It was suspected that the issue is with migadu, but neomutt manages to send everything correctly and further research showed that the issue is within aerc.
See https://github.com/emersion/go-message/issues/165#issuecomment-1447024320
Versions tested: 0.14.0 and c29d08808986dbf19df498b9ee9c4887146266dc
I've sent sample emails to ~rockorager from both aerc and neomutt.
Robin Jarry referenced this ticket in commit 7b8fbe2.