I remembered that some sites use a small spinner on the edge of textarea or something similar to indicate "I am uploading your text to cloud / I am saving your text to disk".

I think it's a good design that tell users your changes are persisted "now" ?

And this can be probably applied to all options that take effects instantly.

Good idea about small save indicator on every change.

Another idea:

When you start typing textarea visually changes style to indicate editing. Once you leave it it changes style back to indicate that this new content is written.

Optionally additionally while editing small X icon might show up and clicking it might cancel the change instead of saving it.