Simple NMOS simulation error. High voltage drop across the nmos when trying to make a MOSFET switch
You should not rely on the default settings for the MOS, since those settings are for IC design, which means voltages of tens of volts are unlikely to be sustained. If you open up the manual and go to LTspice &gt; Circuit Elements &gt; M. you'll see that the default values are Vt0=0, gamma=0, Rd=0, ..., to name a few.

If you want to test a specific model, or subcircuit, you should use that .model card, or .subckt definition appropiately, otherwise all you'll get is GIGO (garbage-in, garbage-out).

Also, you're applying a voltage source directly at the gate of the MOS, and voltage sources have internal resistance (machine) zero, unless you specifically add an external resistance, or set Rser=&lt;...&gt; in the voltage source. It's a zero resistance source driving a capacitance, what could go wrong I wonder?