Could iPad Pro M2 output 1k 120fps video signal to PC through capture card?

It really depends what you're trying to do. If you're editing video, the file can be sent over USB-C port to a destination and. It's just digital data. If you're trying to send a video signal to another monitor, then you're limited to the output resolution and the graphics card in the M2 iPad Pro. The M2 iPad Pro support 6K at 60hz. It does support 4K 120Hz via thunderbolt and USB-C to an HDMI adapter or USB-C to DisplayPort. Then follow the patch below,

iPad > Settings > Accessibility > Motion > Limit Frame Rate > off

Then make sure your monitor is set 120Hz.

No. The M2 iPad Pro tops off at 60Hz.

120Hz is not possible at any resolution on the M2 iPad Pro.

You need an M5 iPad Pro to output at 120Hz.

click here ➜ iPad Pro - Technical Specifications - Apple

Did you really mean to type 1K,1920x1080? Blackmagic Camera, FilmicPro and ProMovie all do 1920 x 1080 at 120fps.