LibreOffice is amazing and I love it and its model of support and free distribution.
Mostly, functionality is superb. But as far as I can see, you can't globally select the text of footnotes. That's weird.
However, it can be done with the help of an extension.
- Download the AltSearch extension by Tomáš Bílek. It's old, but as of August 2024 it works fine.
- Install it by double-clicking the download. LibreOffice will open a menu for you and after installation you'll have to restart LibreOffice.
- With your document loaded, select the new green binoculars icon to open the AltSearch menu.
- Select "Properties/Paragraph style/Footnotes" and double click.
- Select "Find All" and "yes" to the "do you really want to" popup.
- Now all your footnote paragraphs are highlighted. You can close the AltSearch window and use your normal formatting commands to reformat your footnotes.
Many thanks to manj_k who wrote the post that I am totally copying here.