Well, it’s “natural” in that there is a wild form of it, which has been bred and selected over the years to produce the celery we now see in stores (with larger thicker stems, fewer leaves, and milder taste).
I don’t know that it’s been “genetically modified” (GMO) though, or how much of it, if it has though.

“The parent to our modern celery is believed to have originated in the Mediterranean region of Europe and was used by early civilizations for the medicinal properties they thought it contained.”

Celery: A Brief History

https://harvesting-history.com/the-celery/

celery plant history - Google Search

…… And for “celeriac” (celery root, celery knob) which is a member of the same family as celery but is eaten for the large root/bulb, see these:

celeriac history - Google Search

Il sedano è un'antica pianta alimentare. Non sembra essere stato allevato selettivamente in tempi moderni.

Sicuramente non è un soggetto caldo per l'ingegneria genetica con metodi di DNA ricombinante