Solution:
let u=y^(1-n)
du/dx = (1-n) y^(-n) dy/dx
      = (1-n) y^(-n) [
-Py+Qy^n+f]
  =-(1-n) Pu +(1-n)Q +(1-n)f u^(n/n-1)

Separation of variables
[1/(1-n)]Int[du/ { f u^(n/n-1)+Pu-Q}]= Int[dx]= x+ C
Factor out the division and integrates the LHS.
We get F(u,x)=0
then transform into F(y,x)=0.

For n=2, it is very easy to solve. You can try it.