Does Emacs run slower on macOS than it does on a similar machine running Linux? I don’t know. I’ve been running Emacs almost exclusively on macOS for somewhere around 17 years so its performance on macOS, whatever it is, seems normal to me.
Over at the Emacs reddit, staff-engineer says that he runs it on both macOS and on Linux. The Apple machine is, in fact, more powerful than the Linux one but is nevertheless less performant when running Emacs and staff-engineer wonders why.
He received several excellent answers that are definitely worth reading but I especially like the one from totbwf who explains that a large part of the problem is that macOS uses a tiny size for its pty buffers and that this can significantly slow down Emacs when it calls an external process using a process-connection-type of pty. His solution to this is to simply advise functions calling start-process to use pipes instead of ptys. He says that this can speed up these actions by a factor of 10. For Magit, he says that you can get the same result by simply setting magit-process-connection-type to nil.
Even if you don’t want to add a lot of advises to your configuration, it may be worthwhile making this one simple change to Magit if you use it a lot.
To be honest, I have no idea if these fixes will work or not but they’re easy to try if you feel Emacs is too slow on macOS. If changing the connection type helps, I would think that someone would fix it in Emacs core for macOS installations. It doesn’t sound like it would be too hard but one of the problems is that there are few Apple users helping with development.