After the moves 1. d4 d5 2. c4 e6 3. Nf3 Nf6 4. Nc3 Bb4, White can play 5Qa4ch avoiding the Ragozin, Vienna, and Manhattan variations.
After 5. Qa4 Nc6 6. e3 O-O, 7. Qc2 has become popular. Many responses have been recommended.

My notes on this position follows:
ChessPublishing does a great job of covering multiple variations. Kuljasevic likes 7...Re8. Sielecki, Chessable, continues w. 7...b6. Pert chapter 9, continues  with 7...dxc4, 7...Re8!?, and 7...Bd6!?. Parlingras continues with 7...dxc4 and 7...Qe7 - which is new to me.

Another notable position occurs after the moves 1. d4 Nf6 2. c4 e6 3. Nf3 d5 4. Nc3 Bb4 5. cd5 ed5 6. Bg5 h6 7. Bh4

Here Kuljasevic, MC, continued with 7...0-0 and if 8e3 Bf5!? Parlingras follows Pert in recommending 7...Nbd7, a noncommittal move.

There are other moves that cannot be ruled out either:  7. Bh4 g5 8. Bg3 Ne4 9. Nd2 Ng3 10. hg3 c6 and 7...c5