I empathize... but I am afraid I don't have an answer.
I have always enjoyed "learning and building stuff" at work, so much that leaving for vacations was a bit of a trial. However, I think being FI and having more choice (to work or not to work) actually raised my bar for job satisfaction. All jobs have dull and less satisfying moments, but instead of just putting my nose down and working through those bits until I was back in "the flow", now I tend to think "Why am I here, when I don't need to work", "I don't care about Company X high level objectives of selling more boxes, shouldn't I be making the world a better place?". Luckily, for me those periods of time are quite a small percentage of work hours and I very much enjoy the learning and creating stuff... although like you, I am still looking for an exit into something "better" (when I work out what that is).
I was solo consulting from home for a few years, family was good and I was building stuff and earning $$, but because I am not great at setting my own goals and deadlines... I found that I missed the structure and teamwork that a workplace provides and am now more satisfied (although it is not perfect - first world problem! ).
An earlier poster suggested moving to part-time... I think if you can find such a position... it should leave you time to find activities you do enjoy and find satisfying. From my own experience, even though I am strongly an introvert, I think my next non-job needs to include learning and building stuff I care about with a team... if it pays $ then all the better!