Even RE admits rockets return to earth.
The first and second stages usually return to earth but the payload either stays in orbit or heads off on some other mission - say to the Moon, Mars or Pluto.
On the other hand, even RE admits the sun has never had a point of origin on the surface the flat earth plain.
What has the Sun never having "a point of origin on the surface the flat earth plain" got to do with anything.
The usual flat-Earth path of the sun is circling about 5000 km (a bit over 3000 miles) above "the flat earth plain".
The rocket in this photo is continuing to go up but because the distance down-range is increasing so rapidly path seems to head downwards.

Notice also that the width of the exhaust is also
appears to be getting narrower but this is also simply perspective - a row of streetlights will appear to do the same.
Would you suggest that these streetlights are getting closer to the ground?

Obviously not! They appear lower because:
- of perspective and
- the road is curving slightly down.
Note that those lights appear to be getting smaller in size.
And the rocket appear to be getting lower because:
- of perspective and
- the Earth is curving slightly down - the Earth is a Globe!
Note that the exhaust trail appears to be getting narrower.
So why do flat-Earthers claim that
rockets are coming down to earth but insist that
the Sun and Moon are not? That's where the "Double standards" come in!
Flat-Earthers claim that the Sun and Moon, though always about 5000 km above the earth (far higher than that rocket) can appear to not only right down to the horizon but to appear to do
below the horizon as in:
 Sunset at Karumba on August 8, 2007 at 06:25:02 EAST. | |  Sunset at Karumba on August 8, 2007 at 06:25:29 EAST. | |  Sunset at Karumba on August 8, 2007 at 06:25:57 EAST. |
And note again that:
the rocket exhaust trail and the streetlamps both appear to get smaller (narrower for the rocket exhaust trail) but
neither the Sun nor the Moon appear to get smaller from overhead to setting - provided a suitable filter removes the glare from the Sun when it is extemely bright.