The new getTargetName() and getTargetUserIdentity() methods should be used instead (once https://gerrit.wikimedia.org/r/c/mediawiki/core/+/680325 has landed).
The extensions that must be updated before the hard deprecation patch for the core:
WMF deployed
- extensions / CheckUser
- extensions / EventBus
- extensions / LdapAuthentication
- extensions / PageTriage
- operations / mediawiki-config