Answer:
The restraining moment is not taken into account, because the continuous members have been defined separately for the beam and the columns. FE‑LTB only imports the model data and loads (concentrated and member loads) belonging to the defined set of members. The internal forces from RSTAB are not taken into account. It is necessary to model the structural system as close to reality as possible in FE‑LTB.
Due to the introduction of the 7th degree of freedom (warping), the RSTAB internal forces cannot be used. Thus, you "cut" the continuous member and the corresponding loads from the structural system. It is also necessary to define the corresponding boundary conditions (supports, hinges, springs). The calculation according to warping torsion (second-order analysis) then provides internal forces that refer to the load and structural system defined in FE‑LTB.
If you want to consider internal forces from the adjacent components, you have to define them additionally as concentrated loads or member loads in FE‑LTB.
In order to perform the lateral-torsional buckling analysis of the two-hinged frame with FE‑LTB as easily as possible, the entire frame can be defined as a continuous member.
For stability analysis with FE‑LTB, it is necessary to apply imperfections. In this case, the pre-deformation is not only required for each member, but the mode shape is scaled to the specified value.