12.14Why A7 goes to Dm even though Dm is minor

Dominant resolution does not require the destination to be major.

A7:

A C♯ E G

Dm:

D F A

The crucial movement:

C♯ → D

G can move to F.

So:

A7 → Dm

is perfectly strong.

This is why secondary dominants can tonicize both major and minor chords.