I'm not sure if this an issue with go env or with go help environment, but the latter mentions the GODEBUG variable in the first section General purpose environment variables.

However go env -w GODEBUG=gctrace=1 returns an error.

Since, as far as I know, GODEBUG is not used by the go command, go help environment is probably wrong and GODEBUG should be removed.

It may be better, however, to move GODEBUG and the other runtime environment variable in a new section Runtime specific environment variables with the other variables GOGC, GOMAXPROCS, GORACE and GOTRACEBACK.