Enum.reduce/3 is another approach.

data = [abc, ghi, ...]
result = Enum.reduce(data, [], fn x, acc -> if x, do: [x | acc], else: acc end)

# or with a helper function and pattern matching
result = Enum.reduce(data, [], fn x, acc -> maybe_prepend(acc, x) end)
def maybe_prepend(result, data) when is_nil(data), do: result
def maybe_prepend(result, data), do: [data | result]

data = [abc: "abc", ghi: "ghi", ...]
result = Enum.reduce(data, %{}, fn x, acc -> if {key, value} = x, do: Map.put(acc, key, value), else: acc end)

# or with a helper function and pattern matching
result = Enum.reduce(data, %{}, fn x, acc -> maybe_merge(acc, x) end)

def maybe_merge(result, data) when is_nil(data), do: result
def maybe_merge(result, {key, value}), do: Map.merge(result, %{key => value})

Yours seems fine, but another way you could consider is using pipes:

result
|> maybe_abc(args)
|> maybe_ghi(args)

...

def maybe_abc(result, %{matching: true} = args), do: [args | results]
def maybe_abs(result, _args), do: results 

def maybe_ghi(result, %{matching: true} = args), do: [args | results]
def maybe_ghi(result, _args), do: results

Love the reduce approach!

Maybe one day InTheFarFuture™, for example a few weeks before I kick the bucket, I’ll have finally remembered that Collectable exists.