If you are trying to source subtitles for local media players (such as VLC) to use with a personal backup of the files, several prominent online subtitle hubs host user-generated and ripped translation files.
If you tell me you are attempting to use to watch the series, I can give you exact, step-by-step instructions on how to load and fix the subtitles. Midnight Mass (2021) - Titlovi.com
: Because Midnight Mass is a Netflix original limited series, high-quality, professional Croatian subtitles are baked directly into the platform.