@Ross at Play
Grammarly, autocrit, and prowritingaid are all quite good, and free if you accept limits on how much text can be analysed in one request.
Grammarly and I have never gotten along (too many false positives and too few worthwhile corrections to bother with), but with autocrit, which I've used for years, you only get 1,000 words of use 'for free'. Which means, for most chapters, authors would have to spend several days to a week checking a single chapter at a time. While that's doable, it represents a large time commitment without the clear 'ah ha' sense of accomplishment most writers need.
If you like it, I'd urge authors to go for the subscription, but you need to learn which advice to accept and which to ignore. I haven't tried prowritingaid.
However, autocrit, at least, doesn't help me catch my own typos as much as it catches other things, helping me identify repeated uses of the same words and phrases, how often I use words like "said", "that", "then", etc. and other minor details which can weaken your writing.
In the end, it improves my writing, but I doubt my editors even notice any difference when I present it to them.