It’s called Mac OS and is actually a version of UNIX heavily modified by Apple. Linux is basically a copy of UNIX. Mac OS does not have a registry. Mac OS and Windows couldn’t be more different. OSX (the X stands for 10) was the versions of Mac OS that had 10 as the major version number that ended with Catalina.

If you mean people interpret it however it best fits their argument then yes, it’s just like the bible.

My Apple mail kept opening for no reason so I just switched to MailMate. It’s a simple IMAP interface with a ton of backend options and hidden command line settings for the techies, a heavy-lifter email app. It’s a one time payment and is as powerful or simple as you need it to be. Originally written around 2010 and still updated, it’s a very mature program.