https://ask.libreoffice.org/t/how-to-get-rid-of-the-response-alert-red-rectangle/17519/2
How to get rid of the response alert ("red rectangle")? - #2 by peterwt - English - Ask LibreOffice
Feb 29, 2016 - I now have another case where the alert is lit, and I do not know a way to switch it off. I cannot visit the thread via the link given with the response shown...
how to get rid of