On the ribbon, go to Tools > Setups > Banking and select Merchants.
You can select any merchant not required (e.g., PayPal), click Edit and then untick Active. If a Merchant is ticked as not Active the Merchant will not show as a selection in the Merchant Field in Settlements.
You can also select a Fee account for certain Merchants, e.g., PayPal and Afterpay. When entering fee transactions for these Merchants via Settlements, Jim2 will automatically pick up the fee account selected.
Further information