How to distribute the value of one cell evenly in a sequence for the value of another cell?

An approach I would suggest is to distribute the change uniformly between rows 0 and 21 (ensuring that the region outside the reduction zone has the exact number of stiches specified).  Rounding the fractional parts to the nearest integer will give the number of stitches required for each row.  Differencing the count of stitch will return increase/decrease for each row.  I use 365 so the formulas may look unfamiliar but it should convey the idea.

= LET(
    DIFFλ,   LAMBDA(value, value - DROP(VSTACK(0, value),-1)),
    rowNum,  SEQUENCE(1+Rows,,0),
    stiches, ROUND(rowNum * Change / Rows, 0),
    table,   DROP(HSTACK(rowNum, initial+stiches, DIFFλ(stiches)),1),
    VSTACK(table, HSTACK("", "Total change", SUM(TAKE(table,,-1))))
  )