Unfortunately, as the link describes, Netflix only makes this available for a very limited set of languages, while everyone else is stuck with the extremely limited text-based standards.
Frankly, those text-based subtitle standards are quite maddening on their own. Netflix's text-based subtitle rendering seems to support a much wider set of TTML features than what it actually allows subtitle providers to use - so if these restrictions were to be slightly relaxed, providers could start offering better subtitles for anime immediately with no additional effort from Netflix.
What Netflix supports on their main website might not be what they care about, though; you used to be able to watch Netflix on the Nintendo Wii, and they probably still have some users on stupidly old smart TVs.
Also fun fact - subtitles did not work on the Wii at all if you were running a video streaming service!
The BBC spent literally years trying to engineering something that did not result in it being unable to playback video smoothly and failed.
Fast forward to 2025 and BBC's streaming app on ApppleTV only just added subtitles; vastly more powerful hardware but so many restrictions from Apple on how developers use it.