Here is another way you could do this in M.
Adding a column with the row sum

and then select the Item and RowSum column and "unpivoting other columns"

you can then divide the count by the row sum.

You can use the resulting table to create a matrix visual similar to your desired output.

Here is the example M code.

let
    Source = 
    Table.FromRows(
        Json.Document(
            Binary.Decompress(
                Binary.FromText(
                    "i45WMjRQcMnPL1LSUTIEYiMobQzEJkqxOtFKJsjSIGwAVWYMljaDSRsgSZkCsblSbCwA", 
                    BinaryEncoding.Base64
                ), 
                Compression.Deflate
            )
        ), 
        let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Item = _t, #"08:00 - 09:00" = _t, #"09:00 - 10:00" = _t, #"10:00 - 11:00" = _t, #"11:00 - 12:00" = _t, #"12:00 - 13:00" = _t]
    ),
    #"Added Custom" = 
    Table.AddColumn(
        Source, 
        "RowSum", 
        each 
        List.Sum(
            List.Transform(
                Record.ToList(
                    Record.RemoveFields(_, {"Item"})
                ), 
                each Number.FromText(_)
            )
        ), 
        Int64.Type
    ),
    #"Unpivoted Other Columns" = 
    Table.UnpivotOtherColumns(
        #"Added Custom", 
        {"Item", "RowSum"}, 
        "Time", 
        "Value"
    ),
    #"Add Percentage" = 
    Table.AddColumn(
        #"Unpivoted Other Columns", 
        "Percentage", 
        each Number.FromText([Value]) / [RowSum], 
        type number
    ),
    #"Remove RowSum" = 
    Table.RemoveColumns(
        #"Add Percentage",
        {"RowSum"}
    )
in
    #"Remove RowSum"