If you think a tool can reliably detect whether AI was used to write something... well, I have an AI detection tool to sell you.
One writes a post 100% by hand and then asks AI to proofread it. It makes zero changes but adds an invisible watermark. AI detection tool: 100% AI.
One writes a post satirizing AI's writing style. AI detection tool: 100% AI.
One submits an essay one wrote in 2010, more than a decade before ChatGPT existed. AI detection tool: 100% AI.
English is one's second language. One deliberately uses simple vocabulary and consistent sentence structures to avoid grammatical mistakes. AI detection tool: 100% AI.