Use the PSDONJumper header on the NUC mainboard.
Use the PSDONJumper header on the NUC mainboard.
It’s possible using a microcontroller such as an Arduino to manage the power switch. You link the power button to the controller, then write code that closes the actual power switch on the NUC while also turning on the backup PSU via a relay. The process involves wiring and programming, but it should function if done correctly.
You're right, an Arduino might not be the best fit here. With limited room around the NUC and GPU, you'll likely need space for many 40mm or 30mm fans to keep the GPU cool. Still, I'm glad you're considering other options—Arduino is definitely worth checking out!