Linux Kernel: 5.11.2-1-default KDE Plasma Version: 5.21.2 KDE Frameworks Version: 5.79.0 Qt Version: 5.15.2 When using the text annotate module, it is actually pretty hard to insert special character such as mathematical symbols and greek letters. I think it would be a good idea to include some formatting options.
You can use LaTeX for such things. For example, $$E=mc^2$$ or $$\cos \varphi = \tan \alpha$$ https://docs.kde.org/trunk5/en/kdegraphics/okular/annotations.html#annotations-add Adding Unicode symbols is impossible now because of the poppler bug: https://bugs.kde.org/show_bug.cgi?id=305534