Help me

I wanted to know how I can impose homogeneous Neumann boundary conditions for Lagrangre multiplier, using the HDG method for the following problem:

@U/@t = Laplace(U); in Omegax(0,T]
U(x,y,0) = U_0; in Omega
U.n = 0 ; on @Omega

For homogeneous neumann bc you don't have to do anything, for time dependent problems have a look at the iTutorials:
ngsolve.org/docu/latest/i-tutorials/inde...-non-linear-problems

And maybe you could give your topic a descriptive title

Best
Christopher