, 2023

The sum of $P$ and $Q$ is equal to 5, and so $P$ and $Q$ are (in some order) either equal to 1
and 4, or they are equal to 2 and 3.

The difference between $R$ and $S$ is equal to 5, and so $R$ and $S$ must be (in some order) equal to 1 and
6.

Since $R$ and $S$ are equal to 1 and 6, then neither
$P$ nor $Q$ can be 1, which means that $P$ and $Q$ cannot be equal to 1 and 4, and so they
must be equal to 2 and 3.

The only numbers from 1 to 6 not accounted for are 4 and 5.

Since $T$ is greater than $U$, then the number that replaces $T$ is 5.