Hello,
I’ve followed the instructions and looked at some other posts too - can’t seem to get my favicon to work. I copied the png image link into the site icon field in customiser - not sure how to upload a .ico file to media as it won’t select it from my hard drive. What do you suggest?
Thanks for your advice.
Ilka 
Hello There,
Thanks for writing in! WordPress only allows file uploading into the media library if such files meet certain conditions. Specifically, you can only upload the following file types by default in a standard WordPress installation:
.jpeg
.png
.gif
.ico
Maybe your server does not allow it. Please check out this article to know how to add more file types to be uploaded in your server.
https://neliosoftware.com/blog/how-to-upload-additional-file-types-in-wordpress/
Hope this helps.