How to find the max no from an array without using Max() ?

You can create a local variable of Map type and use to data subset to sort the array descending and get the 1st index value

a!localVariables(
  local!listOfInts: {
    a!map(num: 5),
    a!map(num: 6),
    a!map(num: 2),
    a!map(num: 1),
    a!map(num: 10),
    a!map(num: 7)
  },
  index(
    index(
      todatasubset(
        local!listOfInts,
        a!pagingInfo(1, - 1, a!sortInfo("num", false()))
      ).data,
      "num",
      {}
    ),
    1,
    {}
  )
)

You can create a local variable of Map type and use to data subset to sort the array descending and get the 1st index value

a!localVariables(
  local!listOfInts: {
    a!map(num: 5),
    a!map(num: 6),
    a!map(num: 2),
    a!map(num: 1),
    a!map(num: 10),
    a!map(num: 7)
  },
  index(
    index(
      todatasubset(
        local!listOfInts,
        a!pagingInfo(1, - 1, a!sortInfo("num", false()))
      ).data,
      "num",
      {}
    ),
    1,
    {}
  )
)

Can't we achieve this by looping?

where you are looking for looping and why?

You could do this with looping, but max() is by far the easiest and fastest method.  I would also be interested in the use case reasoning to avoid max().

deepakg's example with todatasubset() sorting is a commonly used solution for similar items as well.

Additionally, max value from nested a!forEach():

a!localVariables(
  local!list: {1,3,8,6,5,2},
  
  index(
    reject(
      fn!isnull,
      a!forEach(
        items: local!list,
        expression: {
          a!localVariables(
            local!item: fv!item,
            if(
              count(
                wherecontains(
                  true,
                  a!forEach(
                    items: local!list,
                    expression: toboolean(fv!item<local!item)
                  )
                )
              )=count(local!list)-1,
              fv!item,
              null
            )
          )
        }
      )
    ),
    1,
    null
  )
)

Max with sortintegerarray():

index(
  sortintegerarray({1,3,8,6,5},true),
  1,
  null
)