I've had many years of experience, but essentially only 1 year of experience in any one thing. It's all been pretty random, though notably very little frontend. To get specific without being too specific, in recent years I've implemented a filesystem, made a testing framework, added functionality to a C++ library, created a middleman between kernel space and userspace, etc. The takeaway is I can do lots of things, but am not an expert in anything.
Problem:
Judging by job postings, the two main categories that even remotely fit me are Infrastructure or Backend. The problem is I have huge holes in those categories - I haven't dealt with the setup of CI/CD, created APIs, used Kubernetes, or done anything to do with distributed computing. The extent of my backend web experience were small scale and lived on a single machine. While I have no doubt I could pick things up quickly, the fact is I lack the experience that basically every position is looking for. So far, recruiters won't even give me the time of day. Even if we do have a call, I usually don't even advance to the technical screening.
Solution?
Obviously, need to choose a focus and try to convince someone I am capable of performing. Let's say that's Backend. But what can I do about the massive hole in my experience?
I've been doing Kubernetes tutorials, but the pessimist in me fears that in this job market, there will always be another candidate with actual real world experience that will get the job instead. I would also never be able to simulate a large enough load at home to gain experience in solving scalability issues. Would having played with Kubernetes at home matter at all to prospective employers?
I feel like a fish out of water right now. Has anyone been in my position? How did you solve it?
In terms of skills, yes, you may be helped by figuring out a focus and gaining depth in a particular area. But which area? Here you do need to do another layer of analysis beyond job postings, but you will also need to figure out what interests you, what you would be motivated to do. Which might be more technology or it might at your level of seniority be other areas like business domain or people areas. If business domain or people areas are interesting then you will want to double down on setting up conversations with your network. But if technology is interesting the very best thing to do is the learn in public. Take your lack of knowledge as a strength, start from zero, and use your existing skills to learn how something is implemented, and teach yourself, documenting as you go, to the level of depth that satisfies you. Publish that work. If you have worked at the kernel/file system level you find especially in user space platforms like k8s many oddities and curiosities. Listen to your curiosity and document those oddities. You might actually find something that needs fixing, in that case, submit a PR.
Both of these approaches- reaching out to your network, and following and documenting your curiosity- take time. Doing the job hunt with recruiters does as well. But this way you are growing yourself as an asset, in relationships, and in skills.
HTH. Good luck.
IMO API dev isn't THAT different from what you already do, just a different mindset. Take this with a grain of salt from me though because I only dabble in API dev.
There's an O'Reilly book "Cloud Native DevOps with Kubernetes" that have me a solid grasp on Kubernetes but the biggest lesson from that section was "don't manage k8s yourself" and that was the BEST advice about K8s I've ever seen. Create a free account with the cloud service providers and play around with k8s (ideally after you've run through some guides on CI/CD). This is 100% your "real world experience".
If you're looking to try a new career field I think you'd likely excel in infosec with your background. Take a look at application security and see if that interests you.
I know your pain as I'm on the tail end of what you're going through, but as an outsider looking in it seems you're in a much stronger spot than I am! They're is light at the end of the tunnel!
EDIT: IT needs specialists AND generalists. From one generalist to another, don't be too upset about not being an expert in your domain. I'm a CISSP that struggles with security analysis but can do security management, privacy, and GRC off a fresh bong rip and a four loko+rip it cocktail. THERE IS NOTHING WRONG WITH NOT KNOWING EVERYTHING BECAUSE A GOOD TEAM WILL ALWAYS LOOK OUT FOR EACH OTHER
FWIW, particularly at large companies, I wouldn't have thought the average engineer would be touching Kubernetes, or the build pipeline, or whatever; there's a fair bit of specialisation in large companies. And some companies don't even use Kubernetes; despite appearance, it is not mandatory :)