Long story short, I bought a an HP Omen 30L with a 3090 (prebuilds suck...I know) and due to excessive cpu overheating I decided to rebuild the prebuilt. Replaced everything except the cpu, gpu and memory including going with a fully modular psu since the prebuilt was a non-modular. Everything is working fine except when I shut down the computer the gpu stays on. The light on the card and a single fan stays running all the time unless I turn the psu off. I am a complete loss on what is causing this and and advice would be welcomed.
After taking your advice Jmi, I checked all the psu connections and found it was an rgb problem. When I connected my front fan rgbs it would turn the gpu light and fan on but it didnt properly power down when I shut the computer down. I went in the bios and enabled the Erp which turn all rpg off at shutdown. This included the gpu light and fan. Problem solved!