The AI-powered Denoise feature in Camera Raw is designed only for RAW files. For reducing noise in JPEGs you have to use the traditional noise reduction tool within the Detail panel.
My System: Intel i7-8700K - 64GB RAM - NVidia Geforce RTX 3060 - Windows 11 Pro 25H2 -- LR-Classic 14 - Photoshop 26 - Nik Collection 8 - PureRAW 5 - Topaz PhotoAI 4