I just started to get this error, too. The message appeared in my Wordpress Admin site. I am running Wordfence so I've asked them about it. So far they gave wrong response.
I searched for the URL you can use to solve the problem, but I can't find it using Google. But you can find the URL as follows:
The way to get this message to disappear is to go to your site where the message "unsafe site" appears, and click on the "unsafe site" message shown below.
You will get a dropdown (which I couldn't capture, but it is shown in one of the previous answers to this question). One of the choices is "report as safe."
Click "report as safe," which will take you to a Microsoft URL to solve the issue. You have to fill out a form so Microsoft can check your site out and get back to you.
You need to supply items such as your privacy message to users, what info you collect from them, etc. These things are required by the form.
The message about the site being unsafe remains on the site while they are checking it AND for 24 hours after they decide your site is okay. I sent this link from stackexchange to Microsoft as part of my response and asked them to fix the problem because it wastes a LOT of time on the site owner's part.
I also did not provide my privacy statement. I explained that the site they are saying is unsafe is just my Wordpress admin site, so they fixed the problem and the "unsafe" message was removed.