@Seagull - Can't be certain, but I believe what is happening there is that the macOS is throttling the fps rate for you. While 70-120 fps sounds horrifying for a 60 Hz monitor as all iMacs have, it may not be unless you are getting screen tears. Which Radeon card does your Mac have? My current one would be capable of producing fps well into the high hundreds if it is allowed to, and of course we don't want that.
Origin offers, or should be offering, two different distinct products. The 32-bit and 64-bit ones are different downloads/games entirely, so it would still be required to know for sure which one you are working with. Catalina and Big Sur can only run the 64-bit version, but Mojave can run either on suitable hardware.
My experience with the 64-bit version of the game is limited because it has so many other in-game bugs with it, I really only installed it to confirm some of those, do what we needed to do to make sure NRaas mods work with it (they do) and see what it could and couldn't do. Then I kind of moved on. But I didn't get runaway CPU cycles or fps. Like so many other players, I do get a much better experience with TS3 for Windows run through Bootcamp, if managing two operating systems might be an option for you.
Your other choice, or you might want to do this anyway, is to report your issues on EA's
TS3 for Mac board on AHQ as that is where they are being compiled and looked for. But there may be a solution already there that I wouldn't have known about yet.