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 - 116: Supported
  4. 117: Supported
  5. 118 - 120: Supported

Edge

  1. 12 - 18: Not supported
  2. 79 - 116: Supported
  3. 117: Supported

Safari

  1. 3.1 - 16.6: Not supported
  2. 17.0: Not supported
  3. 17.1 - TP: Not supported

Firefox

  1. 2 - 116: Not supported
  2. 117: Not supported
  3. 118 - 120: Not supported

Opera

  1. 9 - 12.1: Not supported
  2. 15 - 101: Supported
  3. 102: Supported

IE

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

Chrome for Android

  1. 117: Supported

Safari on iOS

  1. 3.2 - 16.6: Not supported
  2. 17.0: Not supported
  3. 17.1: Not supported

Samsung Internet

  1. 4: Not supported
  2. 5 - 21: Supported
  3. 22: Supported

Opera Mini

  1. all: Not supported

Opera Mobile

  1. 10 - 12.1: Not supported
  2. 73: Supported

UC Browser for Android

  1. 15.5: Supported

Android Browser

  1. 2.1 - 4.4.4: Not supported
  2. 117: Not supported

Firefox for Android

  1. 117: Not supported

QQ Browser

  1. 13.1: Not supported

Baidu Browser

  1. 13.18: Supported

KaiOS Browser

  1. 2.5: Not supported
  2. 3: 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