Follow the below mentioned steps to hide / unhide PayPal button from shopping cart page.
Step 1: Login to your Shopify store admin and click on the left menu: Apps.
Step 2: Now click on the Hider app as shown in the below screenshot.
Step 3: Below is the screenshot of how the Hider app's screen looks like. You can use the below highlighted Switch button to hide / unhide PayPal button.