Changes:

several bugfixes, see https://docs.typo3.org/p/sypets/brofix/2.1/en-us/Changelog/Index.html
Hints for upgrading

Upgrading from before 2.1: analyze database and new checking of links is required
Upgrading from before 2.0.0: A CLI command is now used instead of a scheduler task. It is recommended to remove the "old" scheduler task before updating.