There is no shortage of sources on the Queen's Gambit Declined (QGD) exchange variation. It is a very rich line. Sometimes I wonder when published material covers the opening, which one might hope to learn before playing a game, and when it provides middle game examples, problems which you and I must ultimately solve in play.
Recently GM Quintillano (Modern-Chess) has presented the opening from the Black side. In the Nge2 lines, he focuses on ...Nh5 lines. Grandmaster Roiz (Modern-Chess) presents from the White side - in two parts. International Master Tibor Karolyi (Forward Chess, 2018) takes Black's side. It seems to me that he tries to look at all lines, rather than a narrow repertoire choice. This has the advantage that one can look at several lines before choosing one. The opening is also covered well in QGD repertoire books such as the one by GM Nigel Davies. ChessPublishing has provided much insightful analysis.
With so much material, one might expect a lot of overlap. Of course, there is some overlap, but also lines that do not overlap, and even some lines that are not covered!
After 1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. cxd5 exd5 5. Bg5 Be7 6. e3 O-O 7. Bd3 Re8 8. Nge2 c6 9. Qc2 Nbd7 10. O-O Nf8 11. f3.
Roiz, Karoly, Davies, ChessPub, look at 11...Be6. Black develops and intends ...Rc8 with a flexible position. Perhaps a little less popular these days is 11...g6, which achieves many objectives and is also well covered in the literature.
Another move is 11...Ng6. This is an old move found in ECO but largely neglected today. Ruslan Scherbakov, Chess Pub, covers this well in the game Graf-Panchenko, 1986. It is also covered by GM Hammer in a video at Chess24. Hammer said it has been underestimated for a century.
All the moves mentioned, plus 11...b5 covered by Karolyi, have their merit. One thing that I like about 11...Ng6 is that if white does nothing, Black can play 12...h6. White usually continues with the forcing 12.e4 dxe 13.fxe.
Scherbakov and Hammer continue with 13...Be6!? which seems to be adequate in complex play. Not covered as far as I can tell is 13...Ng4!?
Of course, there are many other lines that White or Black may choose. One thing seems clear, the exhaustive book on the QGD exchange variation has yet to be written. It's probably impossible.