Ironically, Google's own Pixel devices are basically the only ones on the market that allow locking the bootloader with your own key [0]. They even follow the recommended bootflow [1], displaying a warning screen with the hash of the installed ROM when you boot the phone.
[0]: https://android.googlesource.com/platform/external/avb/+/mas...
[1]: https://android.googlesource.com/platform/external/avb/+/mas...