Yes in my PC i have both a 2070ti & a 5070ti sharing the same driver. I use a passthru to the 2070 that is connected to a 15khz monitor, so the 5070ti is set a prefered GPU. But as both are Nvidia Cards and share the same 59x.xx driver, it doesnt work. With 58x.xx, no problem with this setup, videos are working. It's really related to NVIDIA Cards and 59x.xx driver problem
The option "let windows decide" use the graphic card that your monitor is attached on.
That is why the Mike trick works, because when you set prefered GPU other than Nvidia, videos are rendered with this graphic card, then passthrough to the NvidiaCard for display