Steps to reproduce the issue

Go to System / Site Templates / Cassiopeia Details and Files
Select the Documentation button - it links to https://docs.joomla.org/J3.x:How_to_use_the_Template_Manager

I have rewritten the Documentation so the link should now be https://docs.joomla.org/J4.x:Template_Overrides

Expected result

J4 Documentation

Actual result

J3 Documentation

System information (as much as possible)

Additional comments

I have been revising the documentation for Joomla 4 to make it more useful in the context of an Index. This is just one of a group of articles on Templates - links at the bottom and more to do.