How do i get to study the impact of body bias on NMOS threshold voltage using LTSpice?
plot for different values

You can use the .step command to perform a up to 3 variables monte carlo simulation
https://www.analog.com/en/technical-articles/ltspice-using-the-step-command-to-perform-repeated-analysis.html#
If you search around some guys posted also some clever tricks to overcome the 3 parameter limit to some extend