Hi,
I did a test with krdc on plasma 5 and plasma 6.0.1
No issue to remote a windows 10 computer outside of my home network.
ultravnc on windows 10 to share / remote the microsoft computer
KDE Plasma Version: 5.27.10
KDE Frameworks Version: 5.115.0
Qt Version: 5.15.12
Graphics Platform: Wayland
KDE Plasma Version: 6.0.1
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2
Graphics Platform: Wayland