Hi Simone,
Thanks for posting in the community.
Normally, the functions FILTER and UNIQUE are currently available only to Microsoft 365 subscribers. Since you mentioned your colleagues have Office 365 Business subscription, I assume users use the Office applications in the screenshot. They can reconfirm the product via File> Account.

If so, please try the following suggestions to troubleshoot the issue further.
- Please try to set Excel into Safe Mode, then check if they can use these functions.
Close Excel, press win + R, in the Run box, type excel /safe, and click OK
- Please try to Repair Office and choose Online Repair. After that, run Excel and check again.
If the issue still exists, I would like to know if the issue exists in a specific workbook or also in a newly created workbook.
When you have time, please feel free and come back to share the updates with us.
Regards,
George