Change text and colour of "Pay with PayPal" button on checkout

2 hours ago, IEn said:

Do you know if I can change the "Pay with PayPal" button at checkout?

This is not possible. You cannot make any changes to the checkout page because code is blocked to prevent interference with secure payments.

Unfortunately, the PayPal integration is very old. Squarespace have invested in other payment processing options (that will bring them more revenue) at the expense of PayPal which, as you say, could process card payments but this is far from obvious.