Ccleaner Version 1.18.30 is reporting incorrect Mac OS

CCleaner is reporting Mac OS X 10.16 whn current version is 11.5.

Mac OS X 10.16

MacBookAir 9.1, Quad-Core Intel Core i7 @ 1.20GHz, 8.0GB RAM

System Software Overview

System Version: macOS 11.5 (20G71)

Kernel Version: Darwin 20.6.0

Boot Volume: Macintosh HD

Boot Mode: Normal

MacBookAir 9.1, Quad-Core Intel Core i7 @ 1.20GHz, 8.0GB RAM

It isn't a bug, it is intentional by Apple.

Big Sur is offically both v10.16 and v11.#, which one you see depends on where and how you look.

It's for legacy/compatibility reasons, see this for a fuller explanation: https://community.ccleaner.com/topic/60444-need-help-understanding-top-right-corner/?tab=comments#comment-328971

Thanks for the complete and interesting answer. I figured it was not just simply overlooked.

P.S. I too, have a taste for beer, Guiness is a favorite, and Kentucky whiskey or a very good Scotch, within my meager limits, that is,