Ask HN: Second Part-Time Job?

I've had a stable (remote) SWE job for company A that pays 6-figures. I feel under-challenged and not super-excited about the industry (marketing), so a few years ago I took on a side-gig at company B in a completely different industry to learn new things, did that for about 8 months (not impacting my job at company A as I would work evenings). Then I quit company B (on good terms), for the following reasons 1)was not super happy with the engineering practices. Code that was produced by other engineers was - to my standards - not of high quality (testing wasn't enforced, random bugs would pop up, lots of patches etc) 2)B was in a complete startup-phase so big uncertainty about the future 3)got burnt out and wanted a shift to focus on open-source projects in the AI domain (which I built and still do, on the side, not making any $ for those currently but being excited about building them)

Now, years later, B has seemingly (survived?), raised $$$ and since I left on good terms they want me back (with higher base offer than what I currently make at A, and higher pay than what I was making last time I worked for them). So my options are

a) stay at a "boring" (remote) job at A (being under-challenged), decline offer from B and have time to work on open-source AI libraries (that really excites me) in hopes of productising those and making $

b) stay at a "boring" (remote) job at A and take on a side-gig at B as part-time in hopes that engineering practices have improved, make a lot more $$$ per paycheck, though sacrificing time spent on open-source AI libraries.

c) quit "boring" (remote) job at A, and join B full-time in hopes that engineering practices have improved and make a bit more $ than at A, and have time to work on open-source AI libraries

What option would be best in your opinion?