There is no function rotate_degrees
in MeshInstance
There is only a member variable
new_mesh.rotation_degrees = Vector3 (0,90,0)
Which you should probably set using the following function
new_mesh.set_rotation_degrees(Vector3 (0,90,0))
Side Note
Most of Godot's variables use the setter / getter scheme and will be get_some_var()
or set_some_var(value)
or is_some_var_set()
and only rarely you will get something random or stupid like _select_int(value)
, however that is being addressed in Godot 4 (at-least what could be deciphered from the source code)