Need Help : Getting column data from one table to other with no relation between those tables,

don't know what solution you are talking about. My solution works just fine. Next time post some data we can grab from your message, not images. 

let
    task_table = #table(
        {"Task_ID", "Planned_Start_Date"},
        {{"TS_1", #date(2023, 9, 20)},
        {"TS_2", #date(2023, 9, 29)},
        {"TS_3", #date(2023, 10, 20)},
        {"TS_4", #date(2023, 10, 8)}}
    ),
    sprint_table = #table(
        {"Sprint_Start_Date", "Spint_End_Date", "Index", "Sprint_ID"},
        {{#date(2023, 9, 18), #date(2023, 10, 1), 1, "S1"},
        {#date(2023, 10, 2), #date(2023, 10, 15), 2, "S2"},
        {#date(2023, 10, 16), #date(2023, 10, 29), 3, "S3"}}
    ),
    rename = Table.RenameColumns(task_table, {"Planned_Start_Date", "Sprint_Start_Date"}),
    combine = sprint_table & rename,
    sort = Table.Sort(combine,{{"Sprint_Start_Date", Order.Ascending}, {"Index", Order.Descending}}),
    fill_down = Table.FillDown(sort,{"Sprint_ID"}),
    filter = Table.SelectRows(fill_down, each ([Task_ID] <> null))[[Task_ID], [Sprint_Start_Date], [Sprint_ID]],
    z = Table.RenameColumns(filter, {"Sprint_Start_Date", "Planned_Start_Date"})
in
    z

Hi Anonymous,

Result:

1.) Delete whole code in 1st step task_table step and replace it with your task_table reference

2.) do the same for 2nd step sprint_table

let
    task_table = #table(
        {"Task_ID", "Planned_Start_Date"},
        {{"TS_1", #date(2023, 9, 20)},
        {"TS_2", #date(2023, 9, 29)},
        {"TS_3", #date(2023, 10, 20)},
        {"TS_4", #date(2023, 10, 8)}}
    ),
    sprint_table = #table(
        {"Sprint_Start_Date", "Sprint_End_Date", "Index", "Sprint_ID"},
        {{#date(2023, 9, 18), #date(2023, 10, 1), 1, "S1"},
        {#date(2023, 10, 2), #date(2023, 10, 15), 2, "S2"},
        {#date(2023, 10, 16), #date(2023, 10, 29), 3, "S3"},
        {#date(2023, 10, 30), #date(2023, 11, 12), 4, "S4"},
        {#date(2023, 11, 13), #date(2023, 11, 26), 5, "S5"},
        {#date(2023, 11, 27), #date(2023, 11, 10), 6, "S6"}}),
    Ad_Sprint_ID = Table.AddColumn(task_table, "Sprint_ID", each Table.SelectRows(sprint_table, (x)=> x[Sprint_Start_Date] <= [Planned_Start_Date] and x[Sprint_End_Date] >= [Planned_Start_Date]){0}[Sprint_ID])
in
    Ad_Sprint_ID