Beelink GT1 and 4K

Joh

Hi,
I have the Beelink GT1 S912 over two years ago (2GB+16GB).
yesterday i received my new 4K monitor : https://iiyama.com/fr_fr/produits/prolite-x4372uhsu-b1/

I connected the GT1 with it by the iiyama HDMI cable. It works in 1080p but not in 2160p and i don't know why.

I have a very good web connection with fiber and HDMI cable 2.0.

The screen resolution stay in 1080p, youtube 4K videos stay in 1080p. Netflix don't offer 4K (I have the premium account with 4K).

Maybe i forgot anything ?

Thanks !
Johann