Explanation:

The Uttar Pradesh Population Policy 2021-2030 aims to achieve a Total Fertility Rate (TFR) of $2.1$ by $2026$ and further reduce it to $1.9$ by $2030$. This policy focuses on various measures to stabilize the population. Option (1) $2026$ is the target year for a TFR of $2.1$, not $1.9$. Options (3) $2036$ and (4) $2042$ are beyond the specific targets set by the current policy for achieving a TFR of $1.9$.