Microsoft Word has a quick way to input unicode characters via a keyboard shortcut: one types the unicode hexadecimal value (e.g. C8) and hits ALT+X, which causes Word to convert the input into the proper character (in this case È).
Many Linux distros actually allow to input unicode characters via a systemwide shortcut (e.g. CTRL+SHIFT+U), while on Windows one has to rely on third party applets, which don’t always play nice with Onlyoffice.
It would be very helpful to implement some kind of keyboard-driven unicode input: it is much faster for power users and quick typers to just use keyboard shortcuts instead of opening a special characters panel and hunting the glyph they want to insert.
On a more general level, it would also be quite helpful to have dedicated shortcuts for small caps, footnote insertion and similar specific tasks, or at least being able to set them in the preferences.