Some of the advice is about expanding yourself, that's good advice.

Some of the advice is about how you milk your current position. You said 6 years in industry so I'll take that at face value. Without promotions I'm assuming you'll be working till retirement even at google. Even an early retirement at 55 or 60 is another 25-30 years of this. Unless you're a hero out of Dilbert fiction you won't be able to milk things that long for many reasons.

I'm an PE at an Amazon subsidiary so I end up getting involved with engineers and teams who are having issues a lot, so this is advice from what I've seen. I've also got a lot of mentees and all of them have hit lulls (short or long) in their careers. This can happen with high performers or career in role type people and those who decide software isnt' for them (managers and go do somthing elsers).

What I see often are people who think that they're treading water but to their managers and leads they're slowing degrading. Unless you are somehow objectively measuring your performance versus your past self this is very likely happening. Lowering motivation leads to slower work. Unless highly trusted, managers avoid giving critical work to unmotivated emplyees. And worst off I usually see people in your place turn salty / bitter / angry. Then things really start to go down hill.

The real enemy here is boredom. As yoda once said "Boredom leads to stagnation, stagnation leads to getting passed by, getting passed by leads to salt, salt leads to PIP."

So now you're 30, pissed at your current job, salty, and not sure what to do. Not a great place to be and it shows in interviews.

I have one friend who this happens to every few years. They get tired of their current projects and get frustrated. Then they stop caring and think they're doing OK. Then about 6 months to a year later they get the talk (pip, letting you go etc). By this point it's usually too late, salt and mistrust have built up and it's hard to break free. (Note: unless you have a manager who is very good at managing your carreer path, they won't notice this slide until year review time when it's likely to late). I have a deal with them now that whenever they feel bored they talk to me and we try and find a good new place for them.

There's nothing wrong with staying at a certain level forever at a company. Some people really like that and love the work life separation. You gain trust with managers and mostly you are able to build what is needed and go home at the end of the day. The deal here is to just make sure you a) aren't bored, and b) you are providing value to the manager/lead and they trust you, talk with them often, c) your company will allow you to stay at that level forever. The last one is a kicker, some companies will manage out people who say stay at SDE1 for more than 5 years as low potential.

I've dealt with others who were actually performing well for their previous role but had stopped growing. They were promoted into place so they would grow and fill the expanded role. After several years of that person (lead) coasting, the team wasn't in a great spot. I got called in to evaluate poor team performance. This ended up with the lead leaving the team and essentially down leveling.

What I'm saying is it can happen to anyone regardless of trajectory.

The fix, however, is hard. You need to find what motivates you. I can't answer that for you. This is the worst / most annoying advice I give my mentees, or hell my teenager. This is because you don't know what you don't know.

Some people find the fix is job hopping. This is a great way to stay well compensated and working on greenfield projects while in a up market. However it does make it quite hard to grow to a senior position as you don't stay long enough to build up those relationships, and is harder to do in a down market. You also take on the risk of the new position not being what you expected.

So again it comes down to figuring out what drives you, as this is the best overall fix. And to that, I'd say what I said at the top differently: "Go Find Yourself". You said you're coasting anyway. Figure out what actually motivates you. Both at home (don't just consume content), and at work (If you still have trust, ask to experiment with roles).