I don’t have a mac but I do know some of the history as I used to: macOS used to be around $130 but macOS Snow Leopard (2009), Lion (2011) and Mountain Lion (2012) were around $20-$30. Since Mavericks (2013) onwards it has been free.
Libreoffice is available, you can install any application you want on a mac provided it’s built for macOS, just like you can on Windows and Linux. You don’t have to install it through the Store either, you can just download it from wherever it is available and install it.
Business model for the mac is that Apple sells hardware, they also have a few applications one can buy such as Final Cut Pro.
The business model for application developers is up to them.
There are tools/package managers for compiling, installing, and upgrading open-source software on a mac, MacPorts and Homebrew.
You can’t run AMD64 Windows applications but there are both free and paid virtual machines (Parallels, UTM) that can run Ubuntu for Aarch64 and Windows Aarch64 in a VM. Funny enough ARM Windows has a translation layer so it can run AMD64 applications. Don’t expect great graphical performance running Windows in a VM. You might also be able to run older AMD64 operating systems (Windows 7) within UTM but it’ll be slow.