If there is anything to get out of this, please get good grades.
Yada yada grades don't matter. Yeah but you know when grades matter most? When you are applying to internships, and especially when you are looking for your first job. Even if a company doesn't admit it, an easy way to filter out students is by a GPA cutoff. For example, in tech, that number is usually 3.5, and for more competitive places, 3.7. While it's true your GPA and what classes you took matter less in mid-career, are you even in a career? No. Also, even though it's not necessarily true that having a good grade in a class implies you got the most out of it (counterexamples: you already knew the content, the standards for the class were low anyway, etc.), it's still a pretty good measure. At the very least, it shows you tried, and you have some semblance of competitive spirit, which is important for most things in the real world, jobs aside.
While this may all sound like parent-talk, the point is, if you don't know what you're doing, you should just work hard to get good grades. The risk of messing up your future prospects with bad academic performance is too high for not just meeting a baseline GPA. This is similar to investing, where most people should invest in the S&P500 if they don't know what they are doing. Yet people are still deluded in thinking they can beat the market and lose tons of money trying to. There is some truth to the slow and steady winning the race in the long term.
There are lots of classes you can take. You can overload and take a bunch of hard ones, you can take easy ones. I was a student who always overloaded, but the one semester I wish I didn't overload (ended up dropping half of my classes to become part-time, by accident), was my Senior Fall, when I was recruiting. Even if you don't have to do interviews every few hours and fly out to a location to do an onsite very few days, it's still very valuable to spend quality time preparing, and deciding what you want to do in the fresh first few years of your post-college life. Also, to iterate the first point again, your GPA does matter, so whatever you are capable of taking to maintain a decent GPA, is how you should stretch yourself in terms of class load.
On which classes to take, my opinion is that if there exist "canonically hard classes," so in CS that would be OS, Compilers. In ECE that would be Embedded. Then you should take them. Granted, there will be lore of legendary classes that turn out to be a flop, but if you take the challenging and "good" classes, you won't go wrong. In terms of if employers wil salivate you having taken OS, I don't think so. But a few months into your job, and you might realize the skills you got from your harder classes ended up giving you a significant edge. Also see https://github.com/CMU-HKN/CMU-ECE-CS-Guide if you're curious about CS and ECE classes at CMU.
The main thing I want to make clear, and it's super obvious, is that:
You can study a class ahead of time
So, concretely. You can study the class the summer or winter before. Read the textbook, look at previous course iterations. It's not cheating, it's just learning it ahead of time. And often, you will find that if you have some exposure to the material (you don't have to read super into it when you do the prep, just skim), you will find you will learn much better when you take the actual class.