Got the same issue here on Kubuntu with when activating transparent background in Konsole with an AMD GPU (flickering of background between transparent and solid).
It only started happening when I switched to Wayland. X11 does not share the issue.
I managed to fix it in Konsole somehow by switching to another apperance theme in the profiles configuration (you might see there that, for some reason, Breeze is duplicated, which I suspect is what responsible for the flickering).
How do I fix the flickering on KDE with transparent themes? (AMDGPU laptop)
*-display...