How to get the Longest Common Prefix (LCP)?

Here you go.

(input1 as text, input2 as text)=>
let
    Inputs = {input1, input2},
    SplitAndZip = List.Zip(List.Transform(Inputs, each Text.ToList(_))),
    CompareValues = List.Transform(SplitAndZip, each _{0} = _{1}),
    FindFirstFalse = List.PositionOf(CompareValues, false),
    KeepFirstCharacters = if input1=input2 then input1 else Text.Combine(List.FirstN(Text.ToList(Inputs{0}), FindFirstFalse), "")
in
    KeepFirstCharacters

Pat

Here you go.

(input1, input2)=>
let
    Inputs = {input1, input2},
    SplitAndZip = List.Zip(List.Transform(Inputs, each try Text.ToList(_) otherwise {})),
    CompareValues = List.Transform(SplitAndZip, each _{0} = _{1}),
    FindFirstFalse = List.PositionOf(CompareValues, false),
    KeepFirstCharacters = if input1=input2 then input1 else Text.Combine(List.FirstN(Text.ToList(Inputs{0}), FindFirstFalse), "")
in
    KeepFirstCharacters

Pat