https://source.android.com/docs/security/features/encryption/file-based

I did not remember correctly, kind of. From AOSP, Android 7 and later use file-based encryption (FBE) rather then full-disk encryption (FDE). FBE is dependant on verified boot, which itself requires a locked bootloader.

Custom ROMs may have back ported FDE, modified FBE, or implemented their own encryption.