The issue does NOT happen with any non-chromium based browser; Firefox is fine.
What I tested:
First I tried installing a new VM on the production host with Manjaro Plasma, but the issue persisted.
Next I tried installing directly (bare iron) on another computer with a totally different hardware configuration. The issue could not be observed.
Then I installed Proxmox on the other computer and created a VM (1CPU/4Cores/8GB Ram, rest default) in proxmox → The issue reappeared.
Finally, I installed Manjaro XFCE on both my production proxmox and the other computer, and the issue did not appear. (This really surprised me)
I have also posted this in the Proxmox forum (sorry, it’s german, but it’s basically the same), but as this seems to be happening only in this specific software configuration, I believe we need to tackle it from both ends at the same time.
At the very beginning, I also tried some software configuration options that I found in other posts, but it didn’t help. I posted about that on reddit with no response.
X11 vs Wayland (firefox now will automatically use either backend … whereas chromium will just be using X11 [or xwayland] without making any config).
Something something ~Hardware Acceleration~ or similar.**
** Technically neither should be hw-accel by default … but firefox will at least try its best, while chromium will be flatly software-only unless you combine a specific conjouring of flags at just the right time when the stars align, and only with certain hardware.
But its just a guess. Could be some blink bug for all I really know.
I have compared the versions of the software components involved in the various distros I had tested. I noticed that only Manjaro/Plasma ran KDE version 6.
ChatGPT told me that Kubuntu 24.10 also uses KDE version 6.
I have been able to reproduce this issue also with Kubuntu 24.10.
→ At this point, it seems to be a problem with the combination of Proxmox and KDE version 6.