Can I use
?

navigator.hardwareConcurrency

- LS

Returns the number of logical cores of the user's CPU. The value may be reduced to prevent device fingerprinting or because it exceeds the allowed number of simultaneous web workers.

IE

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

Edge

  1. 12 - 14: Not supported
  2. 15 - 85: Supported
  3. 86: Supported

Firefox

  1. 2 - 47: Not supported
  2. 48 - 80: Supported
  3. 81: Supported
  4. 82 - 83: Supported

Chrome

  1. 4 - 36: Not supported
  2. 37 - 85: Supported
  3. 86: Supported
  4. 87 - 89: Supported

Safari

  1. 3.1 - 7.1: Not supported
  2. 8 - 10: Disabled by default
  3. 10.1 - 13.1: Supported
  4. 14: Supported
  5. TP: Supported

Opera

  1. 9 - 23: Not supported
  2. 24 - 70: Supported
  3. 71: Supported

iOS Safari

  1. 3.2 - 7.1: Not supported
  2. 8 - 10.2: Disabled by default
  3. 10.3 - 13.7: Supported
  4. 14: Supported

Opera Mini

  1. all: Not supported

Android Browser

  1. 2.1 - 4.4.4: Not supported
  2. 81: Supported

Blackberry Browser

  1. 7: Not supported
  2. 10: Not supported

Opera Mobile

  1. 10 - 12.1: Not supported
  2. 59: Supported

Chrome for Android

  1. 85: Supported

Firefox for Android

  1. 79: Supported

IE Mobile

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

UC Browser for Android

  1. 12.12: Supported

Samsung Internet

  1. 4 - 11.2: Supported
  2. 12.0: Supported

QQ Browser

  1. 10.4: Supported

Baidu Browser

  1. 7.12: Supported

KaiOS Browser

  1. 2.5: Supported
Resources:
WebKit implementation bug
MDN Web Docs - navigator.hardwareConcurrency
Original Proposal