Fairphones are designed and made for Fairphone by T2Mobile which is a Chinese ODM. Fairphones have very poor updates and security. Those devices are incredibly far from meeting the requirements for GrapheneOS and cannot be supported. Fairphones aren't European phones but rather Chinese designed and made devices sold by a European brand. T2Mobile not only designs the hardware but also builds and signs the firmware. Fairphone does very limited engineering and mainly combines AOSP, Google Mobile Services and the firmware/drivers from T2Mobile to make the stock OS. They're not in a position to meet our requirements. T2Mobile doesn't provide good security in practice and would need to greatly improve. Trying to get an ODM to improve security is only realistic with a security-focused organization as their direct customer and Fairphone definitely isn't.

It depends on the level of involvement you're comfortable with. As far as I'm aware, Fairphone are partnered with a Chinese ODM T2 Mobile for the hardware portion of their smartphone products. You can expect they are sourcing the hardware and spares, SoC/subsystem BSP components, peripherals and associated firmware from T2Mobile.

Independence from the Chinese manufacturing hegemony probably means opting for a flagship Samsung, 11-series Pixel or pre-2025 Sony flagship.

I wish fairphone was waterproof, what's the advantage of a repairable phone if a rainy hike will destroy it!

We can solve this if we make a non-Chinese smartphone company. But how?