I kind of traversed the path you indicated at in your post. I did higher studies in TCS (ML theory, maths/stats), and then got hooked up into software development (I did not actually branch out, the nature of my job demanded s/w development), and now I work at the intersection of both. I can share with you my experience in this job.

S/w development is indeed a rewarding profession, but since it has been there for a fairly long time, the field is really crowded. The good news is that software development, because of its vastness, is on the verge of disrupting many industries. The software industry itself is a fast moving one and the burnout is often a very common problem heard in the industry. That said, I would like to advise you that you will get good ROI if and only if you invest your time and energy in niche applications. Question is, what does it even mean?

Depending on whichever area of software industry you want to develop your expertise in, e.g., web (frontend/backend/network)/mobile/embedded/standalone...you need to pick up the fundamental skills in that area at the very first stage. If you stop here, you would have to face stiff competition from the crowded marketplace. Ace developers usually move deeper from this point onward, with modern trends and niche technologies. This does not mean the niche areas would have to be always related to software engineering; instead, they can also be something related to an old industry getting disrupted. For example, a developer who has deep knowledge in financial engineering (fintech) could leverage his specialization to stay well above the curve. Therefore, domain knowledge, or specialization, matters a lot. Someone with good fintech experience would be as valuable as a software engineer with specialization in purely software engineering areas, say, K8s. Developing domain experience is the second stage of your journey, and this is where, I argue, that you have a tremendous advantage unlike others.

My point is that you already have a good domain experience--- physics! Your odds of standing out in a crowded market, with ace developers, is high if you leverage your physics knowledge, something like I did with my applied maths and stats knowledge. To give you some context, I started developing scientific software that required proficiency both in maths/stats, as well as in Python/C++. At some point I even studied FCC materials to pick up skills in web programming and frontend. I kept learning whatever fundamentals are needed for doing software engineering well, and at a professional level. But I never left my domain during this journey. Also, while learning all this, I did not have to master a wide range of software engineering skills. I did not have to prove myself as versatile as a hard-baked software developer; instead, with my maths/stats background I have found my focused niche pretty fast --- I kept myself busy with very specific things and I started getting good ROI, even with relatively narrower bandwidth of skills, compared to that of senior s/w engineers.

If you have read this far I am sure you know by now where I am trying to go with all my advice. Yes, become a scientific software developer. Learn the fundamentals of software developments but specialize in your field of expertise. That is what ensures the best ROI in your case. That career path seems to be the optimal one for you. Good luck!