Can I use the P3020L Mosfet with 5>Vgs>3 without any linear region consequences?
There is no such thing as a transistor &quot;fully on&quot;.
There is &quot;acceptably low resistance between the source and the drain (Rds)&quot; and/or &quot;staying safely away from the saturation region&quot;.
In the datasheet you attached, you may want to look at the &quot;Output characteristics&quot; graph. You will see that at 3V gate voltage, the transistor more or less behaves if the drain current is limited below 6A.
If you want to switch higher currents, you will need higher voltages at the drain in order to keep the transistor out of saturation.
p.s. &quot;Behaves&quot; for a switching transistor is that Rds stays mostly linear and low enough that Vds stays below 1V.
Depending on your project, you may or may not want higher criteria for a &quot;fully on&quot; transistor.