Apply data to all rows in a filtered column

You have a few different options.

You can join the output to a reference of your original table. Steps would be: 1) finalize your original table, disable load; 2) reference your original from #1 and perform the grouping I outlined above, disable load; 3) reference your original from #1, join the categories from #2, enable load

While this is relatively straightforward to do through the UI, it's not as performant as just doing the work inside the group. For that you'll have to implement with M in your formula bar or advanced editor. Here is the full advanced editor snip:

let
    Source = Sample,
    GroupOps = Table.Group(Source, {"Owner"}, {{
        "GroupOps", each [
            grouped_rows = _, 
            group_category = if List.Max(grouped_rows[Tiers]) >= 3 then "Yes" else "No",
            grouped_rows_with_category = Table.AddColumn( 
                grouped_rows, "Threshold Met", 
                each group_category, type text 
            )
        ][grouped_rows_with_category], 
        type table
    }}),
    Combine = Table.Combine( GroupOps[GroupOps] )
in
    Combine

Output: