I am having the same issue with ripping Stargate SG-1. The box to "deinterlace" is greyed out, and cannot be checked. I've tried 1-pass with GPU (1080 TI), 1-pass hardware, 2-pass hardware, and CRF. I've tried different machines, get the same result.
I do not get any flashing, but get some horrible interlacing problems on my 65" 4k OLED TV. But I also see it on my 4k IPS monitor as well.
Would be nice to run this thru deinterlacing protocol to get rid of it, if I can do that, man this would be one killer of a rip.
Thanks,
Michael