In this paper, we investigate the following nonlinear Schr\"odinger equation
with Neumann boundary conditions: \begin{equation*} \begin{cases} -\Delta u+
\lambda u= f(u) & {\rm in} \,~ \Omega,\\ \displaystyle\frac{\partial
u}{\partial \nu}=0 \, &{\rm on}\,~\partial \Omega \end{cases} \end{equation*}
coupled with a constraint condition: \begin{equation*} \int_{\Omega}|u|^2 dx=c,
\end{equation*} where
Ω⊂RN(N≥3) denotes a smooth
bounded domain,
ν represents the unit outer normal vector to $\partial
\Omega
,c
isapositiveconstant,and\lambda$ acts as a Lagrange
multiplier. When the nonlinearity
f exhibits a general mass supercritical
growth at infinity, we establish the existence of normalized solutions, which
are not necessarily positive solutions and can be characterized as mountain
pass type critical points of the associated constraint functional. Our approach
provides a uniform treatment of various nonlinearities, including cases such as
f(u)=∣u∣p−2u,
∣u∣q−2u+∣u∣p−2u, and
−∣u∣q−2u+∣u∣p−2u,
where $2