How do I know if the mods I have in my games folder is broken without playing the game?

Check the websites of your main favourites for updates, to make sure you have the latest. Then you’re probably safe to play.

There is a very comprehensive and helpful post on the General Mods Discussion section detailing broken, updated and cleared mods too.

I know that when there is a bigger update, not just a small patch or whatever, I have to delete the old version of mccc off my computer and get the new version, and...I think enable mods again, because I think they are disabled with an update. Then restart the game. The only way I know of to actually know is to open the game, then if your mods show up in the pop-up they're fine, but if they're not listed in the pop-up they're not. You don't actually have to play the game per se. Anyway, I'm sorry if that was zero help - I'm not super experienced with mods. TS4 is the first game I've played on pc, prior to this I was strictly a console player.