@sun Apparently, even my instance is affected by this bug since I updated from 2.6.3 to 2.8.0. So, this has nothing to do with SPW.
In fact, feld-san already created this issue on Pleroma GitLab mentioning the exact same behavior: https://git.pleroma.social/pleroma/pleroma/-/issues/3323
@feld This doesn't seem to be the general Pleroma behavior, 2.6.3 included the correct value in the CC field for activities. Akkoma doesn't have this issue either. So this is probably a bug introduced after the 2.6.3 release. There's been some changes related to the handling of the CC field and some refactoring in the publisher.ex file, but I couldn't find the exact change/commit that could've caused it.