I cannot find a Standard Bar icon for Format Painter. Where is it on Libreoffice Writer?
Are you talking about the Clone Formatting tool? It seems always a bit misleading, if using terms and phrases from some software tool on a ask & help website of another software, without a short description which functionality is referred by the phrases.
There are differences between painting programs and drawing programs.
LibreOffice has no paint brush.
What do you want to achieve, what do you want to do?
I’ve never used it (except to test this) but I have a format brush showing in the standard toolbar in v6.3.3.2. To use it I click in text of the required format, then click and slide the little paint can icon across the text I want to format.
if it is not showing, use Tools-Customise-(tab)Toolbars-(target)Standard and tick the icon in the functions list, which is the 19th on my list.