You're right that "endgame" is different from person to person, and also in the same person's lifetime.
My current company was something I would have considered endgame at the start of my career. Now it's not.
A company I'd consider to be currently endgame (say, FAANG), may not be 10 years later.
For the sake of discussion, as I mentioned in my original comment, I would simply define an endgame company as one where I'd be satisfied staying for a while without further ambition about finding the next great thing. Where I'd be content doing a helluva great job and not even think about leetcode.
My best friend ended up at one of the FAANGs a few years ago and is doing exactly that. Although he is now afraid that his leetcode skills have atrophied and he'd fail interviews horribly if for whatever (involuntary) reason he ends up having to look for another job. But he has no short term intention of leaving and thus hasn't been grinding leetcode for a while.
I confess that, as someone who has never been primarily a developer (done a number of different things over time), I find this whole leetcode thing beyond strange. I have never in my life studied for interviews other than reading up on a specific company I'm interviewing with. ADDED: And every job since the one out of grad school decades ago has been directly through someone I knew.
You're not the only one. My wife finds the whole thing bizarre. As do my non-techie friends.
My wife's best friend thought it stupid (actually, I agree - it is stupid). Then she started dating a SWE, who is apparently also leetcoding in his spare time.
My current company was something I would have considered endgame at the start of my career. Now it's not.
A company I'd consider to be currently endgame (say, FAANG), may not be 10 years later.
For the sake of discussion, as I mentioned in my original comment, I would simply define an endgame company as one where I'd be satisfied staying for a while without further ambition about finding the next great thing. Where I'd be content doing a helluva great job and not even think about leetcode.
My best friend ended up at one of the FAANGs a few years ago and is doing exactly that. Although he is now afraid that his leetcode skills have atrophied and he'd fail interviews horribly if for whatever (involuntary) reason he ends up having to look for another job. But he has no short term intention of leaving and thus hasn't been grinding leetcode for a while.