In any particular line of work, it’s not necessary to state that you’re a professional, unless of course you’re not.
It’s a bit like those people who begin sentences with “I’m not racist, but…” and proceed to proffer racist opinions, satisfied that they’ve convinced everyone they’re not racist because they just said so.
Or those countries that call themselves “The Democratic Republic of X”. If a country is a democracy, it doesn’t actually need to say so in the title. Everyone knows what a democracy is and can generally see that for themselves. (It’s a system where lots of people who don’t know what they’re talking about decide how to run the country based on incendiary lies by bots.)
There are countries and cultures where the word professional is generally understood to mean that you have a specific official qualification to practise a profession. This clearly gives those who use their services a certain level of assurance that they know how to do a good job. In the English-speaking world, however, professional is often taken to mean simply the opposite of amateur. In other words, a professional is someone who makes a living from their job, as opposed to someone who does it more as a hobby or to earn some extra cash. They may not have passed a specific exam, but their clients examine them every day, and if they fail, they will be out of a job. I don’t know if Leo Messi or Tiger Woods have a certificate to show that they are professional sportspeople, but they don’t really need it by now, do they? In the long term, people can see who is professional and who isn’t, beyond any branding hype.
It also works the other way around when we’re looking for a service provider ourselves. All too often in the social networks you can see people saying something like, “I’m looking for a good professional lawyer/doctor/electrician/etc.” I wonder if there are lots of bad, unprofessional doctors and lawyers saying, “Dang, that job’s not for me, then. Why are there never any offers for bad ones like me? It’s not fair!” Or maybe clients could make insurance claims by finding bad service providers: “I’m looking for a bad plumber or electrician to flood my bathroom or burn my house down. No good ones need apply.”
Professionalism is something you show your clients every day you do your job, not something you simply boast on a CV, certificate, business card or website.
Become professional; don’t just say it.