I’ve uploaded the photos to my desktop, Libre Office 6.2. The pix are there but I need to rotate them for my purposes and the options to “flip” or “rotate” are grayed out.
Check out this video, from 3:18. It is spoken in German, but you can understand it without words.
You should mark the picture beforehand. Right-click on the image and select Rotate or mirror in the context menu.
You can find the documentation here: English documentation | LibreOffice Documentation - Your documentation for LibreOffice
I wish you success!
With me Windows 10 Home; Version 1909; 64-Bit | LibreOffice, Version: 6.4.0.3 (x64).