When Apple introduced the iPhone they required automatic reference counting to be used in Objective-C rather than tracing garbage collection (the language supported both) due to performance reasons (iPhones were significantly slower than Macs). At least Apple seems to think that reference counting is faster than tracing garbage collectors. The compiler can do a lot to remove unnecessary releases and retains. Additionally each retain is just incrementing an integer, and each release is just decrementing an integer and comparing the integer to 0, so the overhead is pretty small.

Metal — it’s a proprietary graphics API made by Apple

I don’t think Apple has every really had great backwards compatibility. Apple’s last PowerPC computers shipped in 2005, and in 2009 Snow Leopard released with no PowerPC support. That’s 4 years of upgrades, which is about the same as it is now for macOS.

It an expression that means “I agree with what you just said”