Every sprint I have sat through ends with a retro. Gather in a room, say what went well, say what did not, write it on a board nobody reopens. Release day gets a postmortem too, eventually, when someone remembers to schedule it.
Source: [Dev.to](https://dev.to/jeelvankhede/the-retro-used-to-wait-for-a-calendar-invite-this-one-did-not-4e5l)