I can see that auto correct is working on MacOS with Edit > Spellchecker > Auto correct spelling enabled but strangely after a period/full stop or a newline it doesn't auto capitalise the first letter like with Apple Notes.
Newline:
Here is some text
i expect the 'i' to be capitalised automatically
After a period / full stop:
Here is some text. i expect the 'i' to be capitalised automatically.