Can I use
?

Filesystem & FileWriter API

- UNOFF

Method of reading and writing files to a sandboxed file system.

Chrome

  1. 4 - 7: Not supported
  2. 8 - 12: Partial support
  3. 13 - 108: Supported
  4. 109: Supported
  5. 110 - 112: Supported

Edge

  1. 12 - 18: Not supported
  2. 79 - 108: Supported
  3. 109: Supported

Safari

  1. 3.1 - 16.2: Not supported
  2. 16.3: Not supported
  3. TP: Not supported

Firefox

  1. 2 - 108: Not supported
  2. 109: Not supported
  3. 110 - 111: Not supported

Opera

  1. 9 - 12.1: Not supported
  2. 15 - 91: Supported
  3. 92: Supported

IE

  1. 5.5 - 10: Not supported
  2. 11: Not supported

Chrome for Android

  1. 109: Supported

Safari on iOS

  1. 3.2 - 16.2: Not supported
  2. 16.3: Not supported

Samsung Internet

  1. 4: Not supported
  2. 5 - 18.0: Supported
  3. 19.0: Supported

Opera Mini

  1. all: Not supported

Opera Mobile

  1. 10 - 12.1: Not supported
  2. 72: Supported

UC Browser for Android

  1. 13.4: Supported

Android Browser

  1. 2.1 - 4.4.4: Not supported
  2. 109: Not supported

Firefox for Android

  1. 107: Not supported

QQ Browser

  1. 13.1: Not supported

Baidu Browser

  1. 13.18: Supported

KaiOS Browser

  1. 2.5: Not supported

The File API: Directories and System specification is no longer being maintained and support may be dropped in future versions.

Resources:
Firefox tracking bug
WebPlatform Docs
HTML5 Rocks tutorial