Very nice question.
I noticed that in your attempts you have given REDUCE() a single constant value in the 1st parameter. Funny enough, the documentation nowhere states you can't give values in array-format. Hence you could use the 1st parameter to give all the constants in (your case; horizontal) array-format, and while you loop through the array of the 2nd parameter you can apply the different types of logic using CHOOSE():
=REDUCE({0,1},SEQUENCE(5),LAMBDA(a,b,CHOOSE({1,2},a+b,a*b)))
This way you have a single REDUCE() function which internal processes will update the given constants from the 1st parameter in array-form. You can now start stacking multiple functions horizontally and input an array of constants, for example:
=REDUCE({0,1,100},SEQUENCE(5),LAMBDA(a,b,CHOOSE({1,2,3},a+b,a*b,a/b)))
I suppose you'd have to use {0\1} and {1\2} like I'd have to in my Dutch version of Excel.
Given your accumulator:
Formula in A1:
=REDUCE(F1:G1,SEQUENCE(F3),LAMBDA(a,b,CHOOSE({1,2},a+b,a*b)))
