Just about any keyboard (mechanical or otherwise) can be used on a Mac. Inside of System Preferences there is a way to remap your command, alt/option, & caps lock, & control key locations if your keyboard doesn't have a way to flash a custom keymap.
I suggest checking out https://reddit.com/r/mechanicalkeyboards and https://geekhack.org.
My first Mechanical was a Das Ultimate 3 with Cherry MX Browns which I used for years on Mac, Windows, & Linux without customizing anything. I've since had numerous keyboards with various switches (Cherry MX Browns, Gateron Browns, Cherry MX Reds, Zealios, Cherry MX Silent Blacks, Topre, Cherry MX Silent Reds, Tealios, and others). I've used full size layouts, TKLs, 75%'s, 65%'s, 60%'s, and more.
My two primary boards right now are 2 HHKB BT's which utilize Topre electrostatic capacitive switches you can learn more about how Topre works here: https://deskthority.net/wiki/Topre_switch. One of my HHKB BT's is used primarily on my MacBook Pro and the other is used primarily on my Windows 10 & Linux desktop. I also have a build in the works for a new Cherry MX Silent Black 60% with a layout that matches the HHKB Pro 2 layout.
Most of the keyboards I've mentioned have actual fully customized keymapping abilities so you can setup layers, remap keys to wherever you want (if you use DVORAK or other layout that isn't QWERTY, etc).
* https://deskthority.net/wiki/HHKB_Professional2
* https://en.wikipedia.org/wiki/Happy_Hacking_Keyboard
I hope this helps. If you have any questions please feel free to reply here or drop me a note on Twitter, Reddit, or Geekhack using the same name (links below).
* https://twitter.com/brianjking
* https://reddit.com/u/brianjking
* https://geekhack.org/index.php?action=profile;u=59613