iPhone 12 and iPhone 13 owners will find iOS 15.1.1 waiting to
install in Software Update. The 1.44GB update contains just one
fix, according to Apple's release notes: iOS 15.1.1 improves call
drop performance on the iPhone 12 and iPhone 13. Apple doesn't list
any other fixes and specifically notes that there are no published
CVE entries for security-related fixes.
Apple previously released tvOS 15.1.1 with unknown fixes.
To download the update, head over to the Settings app, then
General and Software Update. Tap Download and
Install and follow the prompts. The whole process should take
just a few minutes.