This is happening on Plasma 5.15 on Kubuntu 19.04 with GeForce GTX 1060.
I have tried downgrading the GPU driver to 410, and installed KDE Neon user edition, too with the same results.
Is this happening to anyone else?

This is my system info:
Operating System: Kubuntu 19.04
KDE Plasma Version: 5.15.4
KDE Frameworks Version: 5.56.0
Qt Version: 5.12.2
Kernel Version: 5.0.0-8-generic
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-6500 CPU @ 3.20GHz
Memory: 15.6 GiB of RAM
GPU: GTX 1060 6GB

I have posted bug reports on KDE's bug tracker & Launchpad.

Edit: just wanna add some details
In Kubuntu 18.10, where I had 5.15 installed from backports, it happens after waking up from sleep , but it was too painful to use, which gets fixed after reboot. In 19.04 (and also in Neon), it happens after boot, and doesn't get fixed with reboot, although it's less intense and frequent (but frequent enough to get annoying).

Edit 2: I forgot to mention that flickering doesn't happen with Nouveau.

Edit 3: It seems that it's fixed in Plasma 5.16, but it seems to require Qt 5.13 according to this post.

Not NVIDIA problem I think, I have this as well, my screen is flickering whenever I use a web browser (same on Firefox and Chrome), and this machine has a built-in Intel graphic card. Started about 4 days ago, sadly don't know which update is to blame. I also ran into other problems that were kernel related (WLAN), so this might be a tricky one to solve.

Kubuntu 18.10
KDE Plasma 5.15.3
Frameworks 5.54.0
Qt version 5.11.1
Kernel 4.18.0-17-generic

Mamarok wrote:Not NVIDIA problem I think, I have this as well, my screen is flickering whenever I use a web browser (same on Firefox and Chrome), and this machine has a built-in Intel graphic card. Started about 4 days ago, sadly don't know which update is to blame. I also ran into other problems that were kernel related (WLAN), so this might be a tricky one to solve.

Is it just the web browser? Mine's pretty much everything.
https://youtu.be/Gn_dITHQFEs

No, but I very rarely open new applications, my computer just runs with everything I need opening on logging in, except for the browsers

Update: I think it's solved.

After erasing everything related to Plasma & KWin in the .config/ directory, what truly solved it, I believe, was erasing the .nvidia-settings-rc file. I can't believe I didn't think of that until the very end. I was, however, filled with despair before I figured it out.

Good thing I made backups.

For me the final update to the new Kubuntu release solved the problem, I didn't erase any configuration files.