Yes — 什么 and 甚麼 are the same word, both pronounced shénme and both meaning "what". The difference is just character choice, not meaning or grammar.

什么 is the simplified form used in mainland China and Singapore.

甚麼 and 什麼 are both traditional forms. Here it gets a little more nuanced: 甚 is generally considered the original, etymologically "correct" character, while 什 arose as a common substitute because it's simpler to write and sounds the same in this word. Over time 什麼 became the dominant traditional spelling in everyday use — it's what you'll see in Taiwan and Hong Kong newspapers, textbooks, and typing. 甚麼 still appears, especially in more formal or literary writing, or in older texts, but it can feel slightly old-fashioned or bookish to some readers today.

So in practice: if you're writing in traditional characters, 什麼 is the safe, natural everyday choice. 甚麼 isn't wrong, just a bit more formal-sounding. Example: 你想吃什麼？(Nǐ xiǎng chī shénme?) — "What do you want to eat?" — you could swap in 甚麼 there without changing the meaning at all, just the tone slightly toward formality.