Screen trembling (SDL) and not working (Qt)

[risalt]

Hi Tom,
I have built the last release of your emulator under Linux Debian 12, both for SDL and Qt interfaces. My use case is emulating Acorn Electron. I have found that SDL works well, with the caveat that the screen trembles (moves up and down slightly). The fuzziness I understand is by design, but the image should be stable, right? It's a bit distracting right now (see first video attached). I have tested ZXSpectrum emulation and the image is stable, does not show this artifact.
The Qt interface does not work for me, I get the effect of non-tuned analog TV channel, where I can see between the scanlines that something is rendered, but in a not useable way (see second video). I have tested ZXSpectrum emulation and the same error happens.
My monitor is connected to my NVIDIA RTX 2070 SUPER, if that helps, and my desktop manager is Gnome under X11 (not Wayland).
Do you have any idea if this could be my setup or some library misbehaving? I guess that Qt works for the majority of the people, as I have not seen any other open issue on the topic... :)
Thanks a lot for your great work!
Best regards,
Robert.

Screencast from 2024-02-21 04-52-21.webm
Screencast from 2024-02-21 04-53-11.webm