remove an important security update
why would apple ask me if i want to remove an important security (rapid response) update after its installation?
iPhone 13 Pro, iOS 16
You don't say exactly which update. 16.5.1(a) has some issues and was replaced with 16.5.1(c). I think it is also possible that since rapid security responses are issued specially, they might not be fully tested and produce unanticipated issues (as was found with the recent (a) version) and should you have problems with one then you would wish to remove it.
About Rapid Security Responses for iOS, iPadOS, and macOS - Apple Support