The circuit has two oppositely connected ideal diodes in parallel. What is the current flowing in the circuit?

Depending on the battery polarity, one diode will be forward biased (acting as a short circuit) and the other will be reverse biased (acting as an open circuit).Based on the FIITJEE text, $D_1$ is reverse biased.Total resistance $R_{total}=R_{series}=4+2=6\Omega$ (assuming the branch with the open diode is ignored).
$$I=V/R=12/6=2.00\text{A}$$