To filter out FBA shipments from your Purchase Order overview, click on Filters > Default 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.
Then click Apply Filters.
To set this as your default view, click on Filters > Save.
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, hover over name of the filter, click the three dots, then select Apply Preset.