from my understanding of https://help.libreoffice.org/Common/List_of_Regular_Expressions this cannot be done with LibreOffice's internal Find & Replace due to the fact that there is no shortcut of manual line break in the Replace field (\n has an ambigous meaning). But there is an extension at https://extensions.libreoffice.org/extensions/alternative-dialog-find-replace-for-writer calledAlternative Find & Replace for Writer, which can do that:
from my understanding of https://help.libreoffice.org/Common/List_of_Regular_Expressions this cannot be done with LibreOffice's internal Find & Replace due to the fact that there is no shortcut of manual line break in the Replace field (\n has an ambigous meaning). But there is an extension at https://extensions.libreoffice.org/extensions/alternative-dialog-find-replace-for-writer calledAlternative called "Alternative Find & Replace for Writer, Writer", which can do that: