The end goal is to use an N-channel mosfet (SiS176LDN) to drive as strip of LEDs with a stack voltage drip of 20 V and run at 4 A, I chose this specific mosfet because it seemed to be logic driven. It works as expected as a low side switch i.e. gate pulled to ground and to Arduino PWM and source to ground. Though, it doesn't work as expected as a high side switch i.e. gate pulled up to 3.3 V and to Arduino PWM and source to 5 V - the drain is always floating at ~3 V. I can't use a low side switch as the end goal of my project includes using 3 mosfets for 3 strips of LEDs which would introduce multiple ground planes that I don't want to deal with. Hence, high side is the only approach for me. Also, I had selected this specific N-channel as someone recommended it to me and am stuck with it right now, can't change to P-channel even if that's the better approach.
As I've been reading questions on this site, it became quite clear that the Vgs has to be higher than the source voltage. I've tried switching source to 3.3 V and gate at 5 V that doesn't work. But what I'm even more confused about is how people drive the gate at much higher voltages. On the datasheet, under maximum limits, Vds is 70 V and Vgs is +/-12V. So, if someone is switching say 50V a Vgs >50 V is impossible.
Really confused if gate voltage needs to be greater than source and if so, how and why isn't it working with a 3.3 source and 5 V gate. And if the gate voltage can be logic level i.e. 3.3 V why isn't the switching working and the mosfet always on?
Following the commenters solution for the high side, I implemented something similar but with much lower voltages. The 3.3V, 5V and GND all from an arduino. It should be right based on the calculations. When open Vgs = 0 and when closed, Gate voltage ~8.3 hence Vgs = 3.3V. The multimeter reads odd values tho.
I don't have access to a schematics software atm so please excuse this hand drawn schematic, I have used the schematic of the user that answered to test out the high side switch.
On the left side you can see an arduino uno plugged into a laptop.
The n-channel power mosfet : SiS176LDN
and a power supply (from mean well) : which outputs 20V and 3A
Based on the answers below that talk about this working, this should switch on and off with just a 3.3v gate since Vgs is within the range that this should conduct and turn off since the gate is pulled to ground. Instead the output is always on at 20V's