Ask HN: How can a senior software engineer shift to low-level job

I am a senior software engineer with over 8+ years of experience. My main focus in the last years is what the industry calls "Fullstack Developer". I recently realized that I enjoy working on things that are more "low-level" like researching network protocols, linux kernel, filesystems, etc.

I started looking for jobs that intrigue me technically, like for example: "eBPF developer" "Linux Agent Developer' "Linux Internals Developer" "Senior Software Engineer, Linux Kernel" "Senior Software Engineer, Filesystem" "Senior Software Engineer, Protocols"

to some of the above I got referred by friends who vouch me professionally and to some I applied online. Without exceptions, everyone declinded me for not having enough experience related.

I am wondering to myself, as a senior developer with so many projects on his belts in so many different areas of software development (that obviously don't fit a single CV page) why would no one consider me? of course that I'll have some learning curve in those jobs but who won't? It goes without saying but any backend/frontend/fullstack job accepts me without blinking.

What do you suggest me to do? how can a senior software engineer shift his area of expertise without going through being a junior again