What major changes have happened in back end software engineering

So, i have been in a hole for a while, slaving away on a ok paying enterprise solution, while my kid grew and now I want to begin catching up with a sabbatical. I wanted to ask HN about new approaches and stacks i might have missed & would like to look into them / dabble with it, with the intention of dusting up myself with a sabbatical & some exciting project in next 8-10 months & then finally work with some startups along those same lines.

I consider myself a backend engineer (used to be C++, now Java). I mainly enjoy knowing about the underlying system aspects, improving performance & the likes of it.

I havent worked on any hyperscale cloud projects at all either (I know !!)

What are the areas, which have proven themselves well in the past 15 years, which you think i must catch up on ? eg functional / async-io / serverless ? reactive ? wasm / nodejs / go & rust ? Kubernetes ? AI / ML ?

Thanks in advance