(Moving to opening discussion)
When to take on C4 in QGD??

if black Immediately takes the c4 pawn it is NOT the QGD.
it is the Queen Gambit Accepted opening and that opening is a fine acceptable opening; played as you say at the highest level of the game.
now if black quickly takes the c4 pawn and tries to keep it; it can quickly fall for a trap.
most chessplayers know these trap lines; and it you blindly don't consider what white can do; you can find yourself dropping a knight, bishop or rook at the beginning of the game.
this is NO reason to NOT play queens gambit accepted; but it is a good reason to become familiar with the trap; espacially if you play that opening during blitz....

I also think you are misreading wiki; to suggest that when white plays the QGD he will "never" take the c4 pawn. but the focus of the QGD is to look for a positional advantage first
as the game goes toward endgame ofc most pawns will be exchanged.
its kind of one of those situations where you learn about how a given opening works; then try to understand the positional and tactical consequences of your opening choices.

Typically, black tries to wait for White to develop his light square bishop (usually to d3) before taking on c4. This forces white to waste a tempo instead of being able to develop his bishop and capture on c4 at the same time.
That makes sense

I also think you are misreading wiki; to suggest that when white plays the QGD he will "never" take the c4 pawn. but the focus of the QGD is to look for a positional advantage first
as the game goes toward endgame ofc most pawns will be exchanged.
its kind of one of those situations where you learn about how a given opening works; then try to understand the positional and tactical consequences of your opening choices.
Thanks. Also I should've mentioned I know what a QIA (immediate c4 take on move 3) to avoid any confusion. My apologies.
I seen master games when black takes the dxe4 after a few moves in the QGD. But I also read that black shouldn't take c4 pawn at any time in the QGD (Wikipedia)
Am I confusing something?