It is option not obligation. If there's an obligation, it will be stated in the announcement. Chiesa's document for comparison:
Juventus Football Club S.p.A. announces that an agreement with ACF Fiorentina for the temporary acquisition, until 30 June 2022, of the registration rights of the player Federico Chiesa has been finalized for a consideration of € 10 million, of which € 3 million for sporting season 2020/2021 and € 7 million for sporting season 2021/2022.
The agreement further entails:
• The obligation for Juventus to definitely acquire the player’s registrations rights, subject to the achievement of certain given sporting objectives by the end of the season 2021/2022;
• The right for Juventus to definitively acquire the player’s registration rights in case these given objectives are not achieved.