I have been having this problem for years and it has been driving me crazy.
Whenever I want to work with 60 fps video in Vegas Pro, I have always had the issue of the preview in the Video Preview window showing 30 fps, even when I inch across one frame at a time. It always takes two steps forward to advance to a new frame. Likewise, if I move the source video one frame forward or backward and then inch ahead, now every odd frame shows a new image instead of every even frame.
This has nothing to do with exporting, it's only the video preview that's going crazy. It works fine for items from the media generator, or panning across the screen using Pan/Crop, but the source video itself only ever displays at 30 fps no matter how hard I try.
Has this been happening with anyone else? Has anyone else found a solution to this? Currently I'm using Vegas Pro 22.0, running on a Windows 11 laptop with an Nvidia GPU and Intel CPU.