Good morning,
Assuming the table starts in A1 (Jan in B1 and Product1 in A2), use in N2:
=IF(INDEX(B2:M2,1,COUNT(B2:M2))-INDEX(B2:M2,1,COUNT(B2:M2)-1)>0,"Increasing",IF(INDEX(B2:M2,1,COUNT(B2:M2))-INDEX(B2:M2,1,COUNT(B2:M2)-1)<0,"Decreasing","Constant"))
and drag down.
This could probably be condensed, but it works.
Best of luck,
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