On many platforms, you can use the Max Help Center Settings to change the font color, size, and background opacity to improve readability. Physical Media Features
Click the Audio and Subtitles icon (often shown as a speech bubble or "CC").
For the or Blu-ray versions, the subtitle feature is baked into the disc's main menu, often including exclusive subtitles for High Valyrian dialogue to ensure viewers can follow the Targaryen family's private conversations without missing the specific nuances of the fictional language. Subtitles, captions, and audio - HBO Max | Help Center