I just installed an iMac 2012 as a Linux machine for my missus. It has a GTX675M as graphics. I am running Nouveau, as she does not do gaming and only needs desktop.
When logging in to Wayland session with KDE6 (Tumbleweed), the CPU goes to 100% and stays there. X11 is fine.
Is this a known issue with older Nvidia devices, or do I need the Nvidia driver (latest for this card is 470 I believe, so none of the recent wayland fixes)
I remember the exact same issue when I very first tried Wayland approximately one and a half or two years ago. With a GTX1080M (KDE5 back then of cause) all Cores/Threads spiked immediately to 100% and I revered back to X11 until KDE6, but now with KDE6 I have a Integrated Intel + RTX4070M supporting the latest (Nvidia) drivers and the 1080 not anymore.
That even was with the, back at that time newest, Nvidia driver. Never tried with Nouveau. If it is really a Nvidia issue with such a “old” card / no longer updated driver I would not hold high hopes.
But maybe someone else with such a GPU to chime in here.
You might be able to black list the nvidia card an use the igpu but that might hold you back from videos playing at a normal resolution depending on its vram