subtitles “fixed” in them without separate SRT file

can you turn them on and off? meaning, is there a text track embedded in the video file, or is the text actually rendered into each frame?

if the former, you can easily extract them into an SRT file (or another format) using ffmpeg: https://trac.ffmpeg.org/wiki/ExtractSubtitles

I don’t think such things exists. You would need to do some coding work to gule a few tools together. I would do “FFmpeg -> OpenCV -> Tesseract OCR -> tanslator”.