I don’t buy it. As software developers we learn technologies for breakfast. We learn them, and then we forget them. We recollect the wisdom gained and apply it in our next gig using a different technology. It works for mobile development, for frontend, for backend, for infra, for almost anything. I have worked for years with PHP, Apache, Ansible and MySQL. Nowadays not anymore. And in 7 years I’ll be using something…
I seriously think you owe it to yourself to practice learning something new every week. It often takes one afternoon to get a “taste” and small side project to get beyond that.
Every programming language. Is literally just a template for instructions, and every technology just an abstraction over some crud somewhere.