I have quite a few websites in my RSS Reader (I love TinyTinyRSS) and over the last 2-3 years I've seen probably ~10 sites get "makeovers" and every time, the RSS feed I was using for those sites has gone away/broken. Each time I've emailed them to ask "Oh hey are you going to bring back RSS" and of the ~4 that replied, 1 bought it back ~3 months later, the other 3 said "Nope, no one uses it" and the others didn't even reply.
So yes, it's on a steep decline I'd say. I love the "But Podcasts use it" argument! There's what, ~100 major podcast sites people use? Yes, RSS is the backend workhorse that makes it work, but the podcast(content) producers aren't using RSS, they'll be uploading their content to a website. RSS is just the backend magic that makes the podcast clients work.
RSS at most sites seems to suffer bitrot. Sometimes the RSS URL is still http when the site has moved to https etc etc.
It's sad to see the decline of it, because an RSS Reader really is a beautiful thing. But yes, RSS as a way to exposing content to people is dying and used by only a very few hardcore "oldschool" people these days I'd suggest.