Just like the title says, if you type in ‘m’ in a note, it doesn’t automatically get interpreted as a ‘.m’ syllable, and is instead just an empty soundless note when played back or rendered.
As the ‘.m’ syllable exists it just seems like a dictionary oversight to me.
m is a consonant so strictly speaking it can’t form a syllable on its own (and in contrast n is also a consonant but N is a vowel). You can nevertheless add m -> .m mapping to a Japanese user dictionary.
That’s true, but ん isn’t always pronounced or romanized as n. I agree that it’s somewhat of an oversight.