I'm able to encode using av1an (which I believe still uses ffmpeg as its backend) at 3440x1440@30Hz with 10bit color using a mid/high-range AMD 3800X processor.
I'm not sure what might be wrong on your end, but it sounds like ffmpeg's default configs might not be well-optimized yet if you can't encode in real time.
I'm not sure what might be wrong on your end, but it sounds like ffmpeg's default configs might not be well-optimized yet if you can't encode in real time.