I see. I believe the Windows Krita release has a different FFMPEG version but that’s fixable. Download the latest release from FFMPEG, you can get it here https://www.gyan.dev/ffmpeg/builds/ffmpeg-release-essentials.zip
Unzip the archive and look into the folder, there should be a bin folder in there and in it is FFMPEG (the program that does the rendering).
If it’s there go into Krita again, open the render dialogue and press the folder button next to “FFmpeg location”
Navigate to the ffmpeg.exe in the bin folder you just downloaded and extracted.
After selecting and accepting the file selection, you should have more options for codecs.
Try rendering with one of these (but you probably still have to reduce the video width and height)
I’m still wondering what could make openH264 not work, can you tell us what the image color profile and dimensions are? They’re visible at the very bottom in the status bar
