When using any icon set (except for the default Breeze Dark icons) with KDE Plasma’s Breeze Dark theme, the icons on Writer display as black-on-dark-grey, making them very difficult to see. The only solution I’ve found is to just stick with the default icon set when using the Breeze Dark theme.
System info:
Operating System: Debian GNU/Linux 11
KDE Plasma Version: 5.20.5
KDE Frameworks Version: 5.78.0
Qt Version: 5.15.2
Kernel Version: 5.10.0-11-amd64
OS Type: 64-bit
Processors: 12 × AMD Ryzen 5 2600 Six-Core Processor
Memory: 15.6 GiB of RAM
Graphics Processor: GeForce GTX 1060 6GB/PCIe/SSE2