hides the PayPal button on single product pages for products in a specific category

ppcp_remove_single_product_buttons.php

function ppcp_remove_single_product_buttons( $enable_button, $product ) {
    if ( has_term( 'excluded-category-slug', 'product_cat', $product->get_id() ) ) {
        $enable_button = false;
    }
    return $enable_button;
}
add_filter( 'woocommerce_paypal_payments_product_supports_payment_request_button', 'ppcp_remove_single_product_buttons', 10, 2 );