Steps to reproduce the issue

Install Joomla 4.0.0 beta 1
install sample data
login to frontend as super admin
Click Site Settings
Set "Site Name in Page Titles" to After
Save

Expected result

On every page, on the frontend, the site name should be appended to the page title.

Actual result

The site name is only appended to some (most) pages

The exceptions (from the sample data) are:

• Click Site Settings menu item - note that the site title is not appended to the page title
• Click Template Settings menu item - note that the site title is not appended to the page title
• Click to edit a module - note that the site title is not appended to the page title

So it appears that the site name is not appended to the page title when the page is a Edit Form kind of action...

So maybe this is "by accidental design" and is a won't fix ?