PayPal doesn’t charge a fee to add money to your PayPal balance (instantly) via a debit card but I believe that PayPal charges a fee if you are going in the opposite direction - transferring funds from your PayPal balance to your bank account (instantly) but if you do it via standard ACH transfer (which takes 1-2 days) that’s always free
Anybody that has the PayPal World MasterCard credit card (and uses it to obtain 3% in cash rewards via PayPal check out) will tell you that it’s actually to your disadvantage to maintain funds in your PayPal balance because anytime you have any amount of money in your PayPal balance, for whatever reason, PayPal will use that money FIRST and bill the remainder to your checking account thereby forfeiting the 3% in cash rewards on the entire amount (that would have been earned) had PayPal billed the World MasterCard CC (via PayPal Checkout)
It’s incredibly frustrating that PayPal does it this way, but in order to prevent PayPal from doing it this way, I just transfer the exact amount needed into my PayPal balance (right before) I make a PayPal debit card transaction and then any money left over, I then transfer to my PayPal savings so that PayPal doesn’t use those funds for payments that I would otherwise make using my PayPal World MasterCard CC