Merge Multiple Tables with Different Column Names

Table1:

Table2:

Mapping:

Then do the append and column rename:

// Table1
let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WclTSUXICYmel2FgA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t, Column2 = _t, Column3 = _t])
in
    Source

// Table2
let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WclHSUXIFYjel2FgA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column2 = _t, Column3 = _t, Column4 = _t])
in
    Source

// Append1
let
    Source = Table.Combine({Table1, Table2}),
    #"Renamed Columns" = Table.RenameColumns(Source,List.Zip({Mapping[From],Mapping[To]}),MissingField.Ignore)
in
    #"Renamed Columns"

// Mapping
let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45Wcs7PKc3NM1TSgbIclWJ1YKJGcFEnJFFjuKgzkqgJXNQFSdQULuqqFBsLAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [From = _t, To = _t])
in
    Source