Comment by timonoko
Sort-of. Because In Anglo world "aa" is "ä". Even ChatGPT thinks that it ok to use "AA" when making a Finnish morse generator.
In hindsight Maaori is not so bad. Some American Indian writing systems are just pronunciation quides for Anglos (or French). I tried to study Haida some 30 years ago, but it was too complex and miserable, because there was no actual audio clips available at that time.
ChatGPT doesn't think, and I fail to see how it is in any way relevant to the discussion.
Marking a long vowel with a macron has a long heritage, dating back to Ancient Greece at least. Yes, some other writing systems, such as Greenlandic, use a double vowel.
Finnish seems to use ä, ö and å as independent letters, rather like Swedish and Danish, unlike German, were ä, ö and ü are regarded as a, o and u with a diacritical mark. These do not seem to be symbols which mark vowel length.
I don't know Māori, but the Wikipedia page gives the alphabetical order for the language and does not list the long vowels separately, so I assume that, as with German or French, they're regarded as the standard letters with a diacritic mark added.