By default, if a video contains a subtitle track, it will not be displayed during playback on the LG smartphone, but in the user guides we can enable subtitles for videos and also adjust the font size and subtitle style.

Android 9 | LG UX 9.0
Subtitles -  Open the  Settings
Subtitles -  Tap on  General
Subtitles -  Tap on  Accessibility
Subtitles -  Tap on  Hearing
Subtitles -  Enable or Disable  Captions
  1. Open the Settings
  2. Tap on General
  3. Tap on Accessibility
  4. Tap on Hearing
  5. Enable or Disable Captions

LG Instructions