I also was the first engineer of a startup, grew to technical leadership and jack of all trades (infrastructure, developer, manager, architecture, hiring, technical sale, technical support, product, public speaking at conferences, ...), and moved on after 7 years.
The next two companies have been a disaster, I took a role as IC and then as manager, but was miserable in both positions. Too structured. And my experience was too wide. I like to tinker with everything, I don’t have the desire to study the minutiae required to perfectly code a complicated C++ template, and to iterate over a code review until it’s the most esthetically pleasing piece of code. I like to think about the entire system and the business impact.
I’m thinking about trying a PM role, or also a customer facing technical role as sales engineer, since I have played all those in my past.
Like you, I don’t want to work at another startup because I basically burned out, startup life is hard at 70+ hours a week.
I was lucky that my equity turned out to be slightly valuable (slightly more than $1M USD before taxes, so nothing too crazy but better than a punch in the face) so that affords me some freedom since I already had a high savings rate and frugal lifestyle. It’s been much easier to have enough savings to be able to leave when you are unhappy.