CKEditor4 Preview returning 404

Problem/Motivation

The latest version 8.x-1.6's preview doesn't seem to work on CKEditor4. Last working version for CKEditor4 preview was 8.x-1.2. However, 8.x-1.2 can't be installed on Drupal 10 projects.

Steps to reproduce

1. Create Drupal 10 project.
2. Use CKEditor4, and Entity Embed 8.x-1.6.
3. Add Image Embed on CKEditor text format.
4. Create node, add sample Image Embed on CKEditor WYSIWYG, observe preview issue.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes