Re: Origin game transferred to external ssd?
Yes, absolutely you can. If your Mac has USB-C/Thunderbolt 3 ports make sure you get an equivalent drive then the transfer speed will not be an issue.
Which version of macOS are you running? There have been issues with Catalina and installing the game on an external drive. You will also need to keep the Sims 4 user data folder local on your Mac as the game will not read it on an external drive without some jiggery pokery in Terminal.