To filter out FBA shipments from your Purchase Order overview, click on Filters > Warehouse to show a list of warehouses that will be the destination for your shipment.
From the dropdown, click on your non-Amazon warehouse to filter out Amazon shipments.
If you'd like to set this as your default view, you can do this while naming your filter. First click on Filters > Save Filter As.
Then select your filter name and set as default if desired.
If you would like to set a previously saved filter as a default, click on Filters, click the name of the filter, then select 'Use filter <your filter name> as the default'.