This can be changed in Page Properties https://docs.mendix.com/refguide/page-properties/#parameters
Right click somewhere in your Page Editor, outside of the Page itself (so on a greyed out Layout piece for example), go to Properties and change the Page title.
Hi
Luca Villani,
Go to page properties and rename title field.
like below image
Hi Luca,
Do you have a multilingual app? If yes, it could be the issue that you still need to change the title for the other languages your app supports.