Can I use
?

Upgrade Insecure Requests

- CR

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

IE

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

Edge

  1. 12 - 16: Not supported
  2. 17 - 100: Supported
  3. 101: Supported

Firefox

  1. 2 - 41: Not supported
  2. 42 - 99: Supported
  3. 100: Supported
  4. 101 - 102: Supported

Chrome

  1. 4 - 42: Not supported
  2. 43 - 100: Supported
  3. 101: Supported
  4. 102 - 104: Supported

Safari

  1. 3.1 - 10: Not supported
  2. 10.1 - 15.3: Supported
  3. 15.4: Supported
  4. TP: Supported

Opera

  1. 9 - 29: Not supported
  2. 30 - 85: Supported
  3. 86: Supported
  4. 87: Supported

Safari on iOS

  1. 3.2 - 10.2: Not supported
  2. 10.3 - 15.3: Supported
  3. 15.4: Supported

Opera Mini

  1. all: Not supported

Android Browser

  1. 2.1 - 4.4.4: Not supported
  2. 101: Supported

Opera Mobile

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

Chrome for Android

  1. 101: Supported

Firefox for Android

  1. 100: Supported

UC Browser for Android

  1. 12.12: Not supported

Samsung Internet

  1. 4 - 15.0: Supported
  2. 16.0: Supported

QQ Browser

  1. 10.4: Supported

Baidu Browser

  1. 7.12: 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