Change record status: 
Project: 
Introduced in branch: 
10.2.x
Introduced in version: 
10.2.0
Description: 

CKEditor 4 had "Show Blocks" functionality. It didn't exist in CKEditor 5, and since it was a relatively rarely used feature, it was considered fine to add at a later time, if ever.

CKEditor 5 38.1.0 added support for it … and now Drupal core also supports it:

CKEditor 4
Show block
CKEditor 5's equivalent since 38.1.0

Sites that have not yet upgraded from CKEditor 4 to 5 will get it automatically in the same toolbar location as before, thanks to an updated upgrade path.

Sites that have already upgraded to CKEditor 5 can add it manually.

Impacts: 
Site builders, administrators, editors
Site templates, recipes and distribution developers