How to auto number each row and have it locked to that row

Hi there,

I have a table in an excel sheet and I want it to automatically generate the next new row number for that table but also have it locked to that row.
I have used the ROW formula before but when I go to filter the table, i.e. grouping the table by locations, the numbers update, giving each row a new number so that the numbers are in order. I need the numbers to be locked for each row.

The formulas I've tried are:
=TEXT(ROW(A1),"000-000")
=ROW()-ROW(Table2[#Headers])

They work fine but are not locked to the row.

This table is going to have hundreds of rows.

Example of the changing number:
filter example.png