Remove all data related to an application code, when the status equals an error code

I'm glad it worked. You should mark it as a solution in case anyone is searching something similar.

You've mostly understood the code, I'll try to explain it step by step

SelectRelevant = Table.SelectColumns(#"Changed Type", {"Application Number", "Current Status"}),

We get only the 2 columns we're going to work with, to reduce data load.

Select950 = Table.SelectRows(SelectRelevant, each [Current Status] = 950),

We filter the relevant columns for only rows where status is 950

Distinct = Table.Distinct(Table.SelectColumns(Select950, {"Application Number"})),

We get only the [Application Number] column, and because we need any [Application Number] just once, we make it distinct.

Remove950 = Table.RemoveColumns(Table.NestedJoin(#"Changed Type", {"Application Number"}, Distinct, {"Application Number"}, "d", JoinKind.LeftAnti), {"d"})

We join our table as it was before these calculations, with the newfound Distinct table, keeping only non-matches (LeftAnti means anything from left table (#"Changed Type") which didn't match the right table (Distinct)), and subsequently we remove the extra column [d].