Operating System: KDE neon 5.19 KDE Plasma Version: 5.19.1 KDE Frameworks Version: 5.71.0 Qt Version: 5.14.2 Kernel Version: 5.3.0-59-generic OS Type: 64-bit Processors: 4 × Intel® Core™ i7-2670QM CPU @ 2.20GHz Memory: 3,8 GiB of RAM Graphics Processor: llvmpipe Fresh install KDE Neon on Virtualbox to evaluate and it seems double click to maximize title bar is not working. I changed behaviour from "Titlebar Actions" to minimize and still nothing.
Sorry.After double reboot its working as axpected. Virtualbox glitch maybe.