Can I use
?

Upgrade Insecure Requests

- CR

Declare that browsers should transparently upgrade HTTP resources on a website to HTTPS.

Chrome

  1. 4 - 42: Not supported
  2. 43 - 107: Supported
  3. 108: Supported
  4. 109 - 111: Supported

Edge

  1. 12 - 16: Not supported
  2. 17 - 106: Supported
  3. 107: Supported

Safari

  1. 3.1 - 10: Not supported
  2. 10.1 - 16.0: Supported
  3. 16.1: Supported
  4. 16.2 - TP: Supported

Firefox

  1. 2 - 41: Not supported
  2. 42 - 106: Supported
  3. 107: Supported
  4. 108 - 109: Supported

Opera

  1. 9 - 29: Not supported
  2. 30 - 91: Supported
  3. 92: Supported

IE

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

Chrome for Android

  1. 107: Supported

Safari on iOS

  1. 3.2 - 10.2: Not supported
  2. 10.3 - 16.0: Supported
  3. 16.1: Supported

Samsung Internet

  1. 4 - 18.0: Supported
  2. 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. 107: Supported

Firefox for Android

  1. 106: Supported

QQ Browser

  1. 13.1: Supported

Baidu Browser

  1. 13.18: Supported

KaiOS Browser

  1. 2.5: Supported

The HTTP header is Content-Security-Policy: upgrade-insecure-requests. Alternatively, the HTML tag is <meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests">.

Resources:
WebKit feature request bug
MDN Web Docs - Upgrade Insecure Requests
Demo Website