Hi Jiao,

There is no official way to redefine Accelerator keys (including F-keys) in AutoCAD for Mac. You need to edit AcceleratorRoot.cui inside AutoCAD application folder manually. Plus, there is no way to redefine F7...F10 keys in AutoCAD for Mac even with this method.

Please look at this thread:

https://forums.autodesk.com/t5/autocad-for-mac-forum/function-keys-in-autocad-for-mac/m-p/8387230

You can find some useful information about reassigning function keys.

So you can reassign for example F1 key in order to use it as ORTHO toggle. 

Just in case I attached AcceleratorRoot.cui with F1 key redefined for ORTHO toggle. Don't forget to backup original CUI file before replacing it with customized version.