I'm not aware of a third party utility on the macOS to force vsync or cap frame rates. I believe users need to rely on the applications/games they are running to come with that functionality, which unfortunately TS3 does not have.
What GPU does your Mac have and how high are the fps rates running? I am assuming the specs listed in your signature block are not relevant. If it's one of the higher end AMD or Nvidia ones, there may be some relief by way of the equivalent control panels that come with them. If it's Intel, there may not be as much hope here but one wouldn't think many of the Intel integrated graphics chips would be capable of producing runaway overly high frame rates. Even then though, TS3 for Mac runs through a Cider implementation that mimics a scaled down version of Win XP SP2, so it may not be able to honor what the GPU controls, if you have any, are offering.
I haven't played TS3 for Mac myself for more than a few minutes for many years, having opted for Bootcamp instead, but back when I did I had a Radeon HD 6670M graphics card (mid-2011 iMac). There were lots of limitations and issues to be faced with the Mac version of the game, but I don't recall fps rates being one of them back then. On different or more modern GPUs, things may have changed.