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
Step 1:  Open the  Settings
Step 2:  Tap on  General
Step 3:  Tap on  Accessibility
Step 4:  Tap on  Hearing
Step 5:  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