With no @HttpCode() decorator, what status codes does Nest send for a successful @Post() handler and a successful @Get() handler?

POST sends 201 and GET sends 200. Nest's default success status is 200 for every method except POST, which defaults to 201 (Created). You change it per handler with @HttpCode(204) or another code.

"201 and 204" is wrong. Nest never switches to 204 on its own just because the handler returns nothing.