Since this is a support forum, subj is needed in almost all categories – to mark issues as resolved without having to resort to workarounds like writing noise “thank you!” messages or inserting “[SOLVED]” into the topic.
Currently, it’s missing in some of the newer-created categories like https://travis-ci.community/c/environments/bionic and https://travis-ci.community/c/deployment/v2.
The only categories not eligible for that are https://travis-ci.community/c/announcements and, perhaps, https://travis-ci.community/c/early-releases1. But it won’t really hurt (just never use it if it’s not needed) so to solve this issue once and for all, please enable accepted answers globally and be done with needing to think about it.
1This is probably eligible since it’s for limited-time topics that are naturally resolved when the corresponding feature goes out of beta.