iOS 15.2 Compatible With Big Sur 11.6.2????

My iPhone 8 Plus is on iOS 15.2 which was the most recent update. Now, my MacBook Air is using Big Sur 11.6.2 says software update required when I want to backup my phone on it? My boss says not to upgrade to Monterey so that is not an option. How can I backup my phone on my laptop and sync it?