i have HP Omen 17, 144Hz, Nvidia Geforce RTX 2080 8GB, intel core i9.
It has following expansion ports: hdmi; mini display port; thunderbolt 3; 3*USB 3.0
question 1: will this graphics card support 3 external displays at 144Hz?
question 2: how to connect 3 external displays, given that hdmi does not transfer 144Hz as far as i understood, surfing the internet...?
If the system will output to 3 external displays you will need to either try it or contact HP support. There are not many reviews of laptops that test and check the external outputs vs just listing what they are.
It is probably 0 chance it will run 3 displays at 144hz, but again, HP support is your best bet here.