When seeing @return $this it does mean @return self / @return static
In my opinion it is better to use the type and not the variable.
https://codesearch.wmflabs.org/search/?q=%40return%5Cs%2B%5C%24this&i=nope&files=&repos=
Example:
https://doc.wikimedia.org/mediawiki-core/master/php/classHTMLForm.html#adfe69943126042aca2c3fdbb5302bba0
https://gerrit.wikimedia.org/g/mediawiki/core/+/aef18790c6e8eab5d4e2ecee7d8db5549321f781/includes/htmlform/HTMLForm.php#1437
While this looks better:
https://doc.wikimedia.org/mediawiki-core/master/php/classHTMLForm.html#a516b69eed5c82eb271bd596ddd9e4220
https://gerrit.wikimedia.org/g/mediawiki/core/+/aef18790c6e8eab5d4e2ecee7d8db5549321f781/includes/htmlform/HTMLForm.php#968