How to fiercely protect work-life balance?

What if manager is asking more things that you could accomplish?

My advice here is to push back. Here's a good resource about that: "What are good strategies to push back when the deadline is not realistic?"

As an E6, it's expected of you to protect the team and prevent it from getting burnt out. You should get really good at building relationships and project planning so you can accurately estimate how long things should take. If the estimate is way past the deadline, you need to find creative ways to fix that. Here's a good video from Airbnb Engineering Director Rachel Zhao sharing some ideas to help there: How Do Effective Engineering Leaders Help Their Teams Achieve More?

...how to set strict boundaries and if you are not caring as much about level and total compensation?

Your main avenue to put up boundaries is your calendar. You can put a meeting block over lunch and for later in the night. Have a healthy social life so you have hard commitments to hit ("Sorry, I can't review your diff at 8PM, I have dinner with a friend"). More great advice here: [Taro Top 10] Work-Life Balance

My opinion (perhaps contrarian) is that you should be ok with a poor work-life balance temporarily if there is an urgent need in the office. That comes with the territory of being a leader (i.e. a Staff Engineer).

Allocate and broadcast a week where you'll sprint to finish a deliverable. But after that period is done, assuming there's not a fire, you should be comfortable guarding your time and simply telling folks what your turnaround time for code reviews, projects, etc.

If there's a fire all the time, that's another problem

Great related thread where I suggest over-communicating to solve this problem: How do I deal with the pressure of being hired as a Senior SWE and manage my time with family?