That's your own fault (probably). Your Netflix subtitle format is set by the user account. You are using the default, but there are lots of options for making it bigger, or coloured, or outlined. I used it mostly to make them smaller and less noticable, so I could watch English movies that were subtitled in Spanish.
You don't change it in the app you are using if it is on your TV (like using a Playstation or Xbox), it is on your user account on the internet and on tablet apps it sends you to the account on your browser. Your settings there apply to everywhere you watch on your account.
Eta- I'm not quite right. Apple as usual is different. But instructions are here.
https://help.netflix.com/article/en/node/372?ba=GSButtonClick&q=
I keep editing this. That link is not giving the correct instructions for the xbox. I know the options for the subtitles within the xbox app are only on or off. And that only works some of the time, because subtitles are kind of embedded with foreign language movies. But like I said, changing the settings on my account on the internet gives me all kinds of options that are then displayed through my xbox. Possibly apple products might work the same way. It is surprising that the netflix site itself gives the wrong information.