Where I work we tend to write RFCs for fundamental design decisions. Deciding what counts as a "fundamental design decision" is sometimes self-moderated in the moment but we also account for it when making long term plans. For example when initially creating epics in Jira we might find it hard to flesh out as we don't really know how we're going to approach it, so we just start it off with a task to write an RFC.

These can be written either for just our team or for the eyes of all other software teams. In the latter case we put these forward as RFCs for discussion in a fortnightly meeting, which is announced well in advance so people can read them, leave comments beforehand, and only need to attend the meeting if there's an RFC of interest to them up for discussion.

This has gone pretty well for us! It can feel like a pain to write some of these, and at times I think we overuse them somewhat, but I much prefer our approach to any other place I've worked where we didn't have any sort of collaborative design process in place at all.