Solving old problems with new Excel Solutions. This uses the map function to iterate through x and y, then creates a custom lambda function to shorten some of the calculations:

=LET(
    x, X1:X3,
    y, Y1:Y3,
    MAP(
        SEQUENCE(ROWS(x)),
        LAMBDA(v,
            LET(
                r, LAMBDA(a, ROWS(INDEX(a, 1):INDEX(a, v))),
                SUMPRODUCT(
                    INDEX(x, SEQUENCE(r(x))),
                    INDEX(y, SEQUENCE(r(y), , r(y), -1))
                )
            )
        )
    )
)