Otdfbt

I have a smart diagram:

beginframe
 begincenter
 smartdiagramanimated[descriptive diagram]
 Style,
 Style,Define shapes, colors, shading,
 and line styles for nodes and arrows,
 Position, Place nodes using a matrix,
 relative or absolute positioning,
 Relation, Insert edges or arrows
 between selected nodes,
 Label, Add labels on edges or arrows
 endcenter
endframe

Which produce the following diagram:

But my problem is that I want 2 things:

1- I want the first "Style" item to be a rectangle like the ones down instead of being in a circle like that and to be in the center.

2- is there any possibility to add arrows in this specific descriptive diagram which links each circle and rectangle with the next one, maybe something like this will be helpful:

The method from leandris' link does work if one uses the names indicated there. Let me start with a version in which we get rid of the unwanted node by overpainting it. (Below there is an alternative, which is arguably more elegant but also more "hacky" and that will cease to work in its current form if the package author changes the counter from xi to something different which may not be a Greek letter.)

documentclassbeamer
usepackagesmartdiagram
usetikzlibraryoverlay-beamer-styles
begindocument
beginframe[plain]
centeringtikzsetevery picture/.append style=remember picture
smartdiagramanimated[descriptive diagram]
 ,blub,
 Style,Define shapes, colors, shading,
 and line styles for nodes and arrows,
 Position, Place nodes using a matrix,
 relative or absolute positioning,
 Relation, Insert edges or arrows
 between selected nodes,
 Label, Add labels on edges or arrows
begintikzpicture[overlay,remember picture]
only<1>-module-title1.north)
rectangle ++ (-1.8cm,-1.63cm);
fill[white] (module1.west|-module-title1.north)
rectangle ++ (-1.6cm,-1.63cm);
foreach X [count=Y,evaluate=Y as Z using int(2+2*Y)] in 2,...,5
draw[line width=1mm,-latex,visible on=<Z->] (moduleY.south) -- (moduleX.north);
endtikzpicture
endframe
enddocument

As usual with remember picture, you need to compile twice.

ADDENDUM: Just for fun: this attempts to address the question

how can one "hack" packages like smartdiagram when they do exactly
what we want except for a small detail?

One conceivable way of accomplishing this is to locally redefine the styles. In the following code the first round node gets removed without being overpainted. This is achieved by looking up the counter in the smartdiagram manual (which is really extremely well written). This counter is, as of now, called xi (which may eventually lead to problems if some user wants to use the Greek letter $xi$ in their code, they may be a bit surprised, so Claudio, if you read this, please let me know if you rename the counter so that I can modify the answer accordingly ;-). So all we need to do is to say

description title/.append style=/utils/exec=ifnumxi=1
pgfkeysalsoopacity=0,every shadow/.append style=opacity=0
fi

such that the first item remains invisible. This is the complete code.

documentclassbeamer
usepackagesmartdiagram
usetikzlibraryoverlay-beamer-styles
begindocument
beginframe[plain]
centeringbegingroup% we want to keep these hacks local
tikzsetevery picture/.append style=remember picture,
description title/.append style=/utils/exec=ifnumxi=1
pgfkeysalsoopacity=0,every shadow/.append style=opacity=0
fi
smartdiagramanimated[descriptive diagram]
 ,blub,
 Style,Define shapes, colors, shading,
 and line styles for nodes and arrows,
 Position, Place nodes using a matrix,
 relative or absolute positioning,
 Relation, Insert edges or arrows
 between selected nodes,
 Label, Add labels on edges or arrows
begintikzpicture[overlay,remember picture]
 foreach X [count=Y,evaluate=Y as Z using int(2+2*Y)] in 2,...,5
 draw[line width=1mm,-latex,visible on=<Z->] (moduleY.south) -- (moduleX.north);
endtikzpictureendgroup
endframe
enddocument