If user has installed KDE integration package he cannot use shortcut Ctrl + Shift + u for inserting Unicode keys.
It occurs on every LO installation (via homepage or repository). Users must avoid to install this package and use GtK integration on KDE desktop.
Steps to Reproduce:
1. Install LibreOffice (any version).
2. Install KDE integration pack.
3. Start LibreOffice (writer).
4. Press Ctrl + Shift + u keys for inserting Unicode key.
5. Type Unicode code.
Unicode key inserted.
Nothing happened, user types ASCII keys.
User Profile Reset: Yes
Build ID: 1:6.4.4-0ubuntu0.20.04.1
CPU threads: 2; OS: Linux 5.4; UI render: default; VCL: kf5;
Locale: cs-CZ (cs_CZ.UTF-8); UI-Language: en-US
From how I understand it, that's not an issue on LibreOffice level, but further down the stack, s. e.g. KDE bug https://bugs.kde.org/show_bug.cgi?id=103788 .
For me, it doesn't work for other KDE/Qt applications (like Kate) either, while it does work for Gtk applications (like Gedit).
Once a solution for KDE Plasma/Qt/... has been implemented, it should work "automatically" in LibreOffice with KDE integration as well.
As mentioned in https://bugs.kde.org/show_bug.cgi?id=103788#c19, using some input method tool like IBus should make it possible to make it possible for now.
Hence, closing as RESOLVED NOTOURBUG.
In case I'm wrong and you know more more of how it's supposed to work, please reopen and add more information here.
Note it doesn't work e.g. with the "gen" VCL plugin either, i.e. when starting LO with environment variable SAL_USE_VCLPLUGIN=gen set.