All the rows after last "8" in PQ

I guess you need table with values after last 8 in Numbers, not column with above values and null before.

Not sure simple way with UI only exists. I'd modify a bit what OliverScheurich  suggested by using Index, not Number in conditional column.

• Add Index column
• Add Conditional Column (if Number equal 8 then Index)
• Fill this column down
• Group By this column without aggregation
• Sort result descending and keep first row
• Keep only column with Data
• Drill table down
• Filter on first row with number 8
• Remove all columns but Number

With M-Code it could be much easier

let
    Source = Excel.CurrentWorkbook(){[Name="Tabelle1"]}[Content],
    Result = Table.RemoveFirstN( Source, List.PositionOf( Source[Number], 8, 1) + 1 )
in
    Result