@several who they don't pair and ask people to explain why - you are revealing a lack of understanding of earlier functionality. As several have noted - actually, in iOS 15 and macOS 11, it was possible to pair Bluetooth on iPhone with a MacBook Air M1 as a bluetooth device (and also on Apple intel macs) - functionality which continued to work when upgrading to macOS 12. in iOS 16 and macOS 13 as of today's date latest updates, it is now broken.
As others noted as well, the pairing of an iPhone as Bluetooth device on a Mac in this manner, made it possible to use applications sold in the App Store and approved by Apple such as Type2Phone from Houdah, allowing a user to quickly touch-type on a phone from a MacBook's keyboard, without having to buy a separate Bluetooth keyboard. Was very helpful for messaging apps.
It seems that Apple has changed the functionality and dropped a supported feature *without* making this clear. Worse, AppleCare support techs "Genius" level (i.e. entry level!) don't know this and so waste users time suggesting to reset network settings on Mac or Iphone, re-install macOS, reset all settings, etc., if one does have support.
Apple can do what it wants but it is legitimate to complain about a premium product company that markets for caring about the user experience, doing this. Also, increasingly, Apple *forces* users to update macOS and iOS. For example, my watchOS, I couldn't update a security fix, without updating to a major new version of watchOS which also required updating to a major new version of iOS 16 first, breaking bluetooth pairing on Mac-to-iPhone. Until recently, each device would receive many years of security updates to the earlier OS versions.
The type-to-phone apps also are still in the App Store without any notice, a store Apple runs at great profit. Houdah has graciously edited their App Store comments telling users not to buy the app until this is fixed if you have newer macOS / iOS, although it works on older systems still. Houdah - a great company! Now that's user-friendly support. Their products are extremely useful and Apple increasingly breaks the functionality / makes it more challenging for developers.