Janaque That looks more or less like what I'd expect, and it doesn't appear that you have anything extraneous on your C drive, at least not anything large enough to be worth deleting. Program Data might have some extra files you can flush, but I wouldn't suggest doing so unless you don't have the associated app(s) installed at the moment. Some of the data in that folder is junk, but some is important.
I will say that you could probably delete anything EA App-related, but rather than doing so by hand, I'd suggest using Revo Uninstaller (the free version) to remove the App and then reinstalling it. That only applies if there's enough EA App-related data in there to be worth removing in the first place though.
It's fine to keep your SSD at around 25-35 GB free. Lower than 20 GB isn't an immediate problem either, in that it's fine as an interim state, say while you're copying files around or running an update. The real problems happen below 10 GB or so, and if you're below 20 when Windows wants to install a feature update.
You can also uninstall Sims 4 and reinstall it on your external drive if you'd like. I would suggest doing a clean uninstall, as I mentioned earlier, in case some of the data in Program Data can be flushed. You can also redirect the user folder to the external drive by creating a symbolic link, as described here:
https://crinrict.com/blog/2020/02/moving-windows-documents-folder-to-external-drive-via-symbolic-link.html
You don't need to do both, but you might want to for peace of mind. Or you could do one now and the other at some later date if it becomes necessary. Regardless, it would be best to create folders on the external to keep things separated. For example, you might install Sims 4 into D:\Games and move the user folder into D:\Sims Data. The names don't matter as long as neither is "The Sims 4."
Feel free to ask more questions about any part of the process.