An odd definition of unprofessional. Building and testing a site for running without JS is a non-zero cost. But I've never seen usage stats that show that demographic above 1.5% of the browser market share – and those are old stats. It was sub 0.5% for the sites that I ran at the time (2018).

I don't mean to sound flippant, nor do I mean to insult anyone's favorite browsing style, but insisting on this might be shouting into the wind? I could never make a business case for it, at least.