This has been happening since December and is an FCP 10.7 bug which has not been fixed. It does not relate to the OS directly. It happens on Sonoma and Ventura (Tom reported this) but is mainly reported for Sonoma primarily I presume because those who tend to update FCP also tend to update the OS.
It is a complex bug. It is only observed on some computers and not others so some Intel Macs and M1 Mac Minis seem to be the main ones affected. It affects some ProRes Raw files and not others even from the same camera. It relates to frame size and not frame rate so, for example, 4.1K ProRes Raw files from the Nikon Z8 and Z9 are affected regardless of frame rate but not 5.3K ProRes Raw files from the same cameras.
It will take an FCP update to fix. I think it is pointless to try to go back to an earlier version of the OS. The only fix for affected computers is to install FCP 6.x. There are workarounds such as using Compressor to transcode to ProRes.