The work is interesting, though never novel.
Everybody I know tells me programmers should change jobs every 2 years, but I feel like maybe I struck gold the first time?
I advocate every 6-12 months, even (or especially if) you're happy where you are. There's virtually no downside to doing this except for an unpleasant vacation day. Worst case is you still have your job you like. Best case is you get an offer that gets you a raise (either where you are or with a better company).
(Doing this I've gotten about a 10% raise every year for the past ~8 years - sometimes changing jobs but usually just presenting an offer to current employer - and I'm not a rockstar interviewer or anything.)
Enjoy your good fortune and be grateful. A lot of people hate their jobs. Even programmers.
Just make sure you're always able to get a new job if necessary. Basic stuff like keep learning something useful, don't tie yourself too much financially, etc.
It's not about corporates or start-ups it is as you say about sustainability.
It's rough that their is a perception that cutting edge work has to happen either in corporate or start-up or the games industry.
I suppose to some extent that is actually true, but there is a middle ground.
You can define that for yourself and it sounds like you are doing.
You already have it figured out :-)
+ A company that gives me a good work/life balance + Regular WFH or preferably be fully remote + Interesting tasks, in a relatively stable environment
Most of my peers seem to want the same thing as well. While I've done the crazy workweek startup thing before, it burns you out and it's simply not sustainable. I don't have a single peer who still works in startup land.