Here's a PSA for anyone trying to configure Drupal 8/9 behind a reverse proxy in order to create canonical URLs (in head, and header) that preserve the original remote request protocol - HTTPS.

The Drupal 8 team have done a brilliant job of getting Layout Builder stable in core. Here's a tip on how you can transition to a layout builder-based theme while keeping your existing region-based and global block-based theme active for as long as needed.