Autocorrect is also going to be available soon in Google Docs comments. Instead of just indicating that word is misspelled with a red underline, Google Docs will now just correct the spelling.
According to Google's announcement, Autocorrect and Smart Compose will be on by default for all users. Autocorrect and Smart Compose can be disabled by individual users.
As is usually the case with updates to Google Docs, these new features are available now for some users and will be rolled-out to all users over the next few weeks.