You’re using the latest nightly build of ffmpeg from gyan.
It may be better to use the current formal 7.1.1 release:
https://www.gyan.dev/ffmpeg/builds/packages/ffmpeg-7.1.1-essentials_build.zip
Krita now has ffmpeg built in to it and has done for some time.
Instead of using an external ffmpeg, you can use the built in one at:
C:/Program Files/Krita (x64)/bin/ffmpeg.exe
Does the video file you produce play ok using the media player or image viewer on your computer? If it doesn’t then that needs to be sorted out first.