Autocorrect doesn't always work; it very rarely shows red underlining and when it does it doesn't always give suggestions

spencer66 wrote:

macOS Catalina. Autocorrect is turned on (all three boxes are ticked) and it shows red underlinings sporadically and it doesn't always give suggestions.

I think this is the nature of the beast.

You can Control click the red warning—this should offer suggestion.

ex.

badd to the bone

Set up auto-correction and add words to your spelling ...

Check spelling and grammar on Mac - Apple Support

Even Grammarly won't just automatically correct mistakes. It too applies a red underline to input transgressions and offers one or more alternatives for replacement when you click on the underlined content. I am using it right now as a Safari extension while typing this content.