It is. They add it automatically on mobile but you can delete it. And it's never on desktop. Just tried to send from both clients and didn't have any extra added to the message.
I even had brought up the browser's dev tools and tried to disable that setting but with no luck. It might had been a A/B test, or specific only to my country, but the point remains that it was a separate setting than the signature and it was impossible to disable it without paying. On desktop.