I’m not 100% positive as don’t regularly use these settings, but I think that is how macOS indicates it has auto-corrected your text. What has me confused is that I thought that just showed up briefly after it fixed a word, rather than sticking around like that.
Well here are some things to try:
Edit/Spelling and Grammar/Check Gramar with Spelling
In the Corrections preference pane: Correct spelling errors as you type.
I find the “stick around” behavior varies app to app. I’m certain it has something to do with the underlying txt entry object. For example, in messages the dots do not stick around much. In scriv they do. In mail they do. In safari posts to the forum they do not.
If it wasn’t for the messages/mail/safari differences I would say it’s an apple internal API thing but there it is acting different in apple internal apps.
Did you dictate this text by any chance? This is a feature of macOS. When you use it’s dictation feature, it places blue dots beneath text that it isn’t entirely sure of. You can then Ctrl-click on such sections of text to choose alternative suggestions. (Unfortunately there’s a bug I’ve just noticed whereby Scrivener isn’t showing those suggestions, owing to its custom contextual menu - I’ve fixed that for the first update.) I’m afraid I have no idea how to tell the text system how to accept the changes and get rid of the dots, though! The easiest way I have found is to simply click on another document in the binder and then click back again. I can’t find any documentation from Apple on this. (Dictation is a standard part of the macOS text system rather than something specifically provided by Scrivener.)
I bought Dragon when I was still using Snow Leopard which didn’t have OS dictation. I was lucky enough to find a copy of v2.5 (wifi) for £25 instead of the £200+ it used to cost new.
While the Mac OS dictation is pretty accomplished (and free, and written by the same company - Nuance - that does Dragon), the beauty of Dragon is that you can do so much more with it : for example you can move forwards and back to correct mistakes, you can go into Spelling Mode, and best of all, you can train it in words and phrases it doesn’t seem to “get” at first when you say them, and teach it unusual words, names, place names, nicknames, etc.