If you're just to rotate your point within a polygon layer that has a single rectangle, you can use something like the following:
with_variable('centroid',centroid(aggregate('Rectangle','array_agg',@geometry)[0]),with_variable('distance',distance(@geometry,@centroid),with_variable('azimuth',azimuth(@geometry,@centroid),project(@centroid,@distance,@azimuth))))It relies on the fact that a rotation within a rectangle is just projecting the point from the centroid, the same distance and same angle again.
