Microsoft Excel is a Microsoft product - not Apple.
For iPad devices with a screen larger than 10.1”, the Microsoft Office Apps, such as Excel, require an active Microsoft 365 Subscription to enable full functionality. If you don’t have an active Microsoft 365 subscription, functionality is limited to opening and reviewing existing documents.
As consequence, Microsoft is offering a 30-day trial for Excel (and all other Microsoft Office Apps). The trial licence and subscription are valid cross-platform - and can be used with your iPad, Windows PC and Mac computers.
If you already have an active Microsoft subscription, ensure that you sign-in with your Microsoft Account to unlock full functionality of your Microsoft Apps on iPad. Signing-in with your Microsoft Account will suppress the trial notification/offer.