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 - 105: Supported
  4. 106: Supported
  5. 107 - 109: Supported

Edge

  1. 12 - 18: Not supported
  2. 79 - 104: Supported
  3. 105: Supported

Safari

  1. 3.1 - 15.6: Not supported
  2. 16.0: Not supported
  3. 16.1 - TP: Not supported

Firefox

  1. 2 - 104: Not supported
  2. 105: Not supported
  3. 106 - 107: Not supported

Opera

  1. 9 - 12.1: Not supported
  2. 15 - 90: Supported
  3. 91: Supported

IE

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

Chrome for Android

  1. 105: Supported

Safari on iOS

  1. 3.2 - 15.6: Not supported
  2. 16.0: Not supported
  3. 16.1: Not supported

Samsung Internet

  1. 4: Not supported
  2. 5 - 17.0: Supported
  3. 18.0: Supported

Opera Mini

  1. all: Not supported

Opera Mobile

  1. 10 - 12.1: Not supported
  2. 64: Not supported

UC Browser for Android

  1. 13.4: Supported

Android Browser

  1. 2.1 - 4.4.4: Not supported
  2. 105: Not supported

Firefox for Android

  1. 104: 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