Comment by Johnny555

I think you'll find that you agreed to it somewhere in their voluminous terms of service.

I looked it up and indeed, it's in section 1, paragraph C:

Your Device will periodically check with Apple for Apple Software Changes. If a change is available, the change may automatically download and install onto your Device and, if applicable, your peripheral devices. By using the Apple Software, you agree that Apple may download and install automatic Apple Software Changes onto your Device and your peripheral devices.

https://www.apple.com/legal/sla/docs/iOS26_iPadOS26.pdf