When implementing the Official PayPal Plus extension on a Magento Open Source version 2.3.3 I encountered the same problem:
When both the PayPal Plus Extension and the PayPal Express Checkout Extension are enabled, both extensions load their respective payment options in the checkout. All PayPal related payment methods are thus duplicated in the checkout.
The configuration settings of the PayPal Express Checkout Extension in the admin interface have no effect.
While reading the Magento Open Source 2.3.4 Release Notes, I did not find a solution to the problem, but I did find a mention for this behavior:
- Magento no longer displays the PayPal Express Checkout button on product pages or the shopping cart when the Display on Product Details Page and Display on Shopping Cart (Advanced Settings) settings are disabled.
So this is a known bug and an update to the current version 2.3.4 should fix the problem.
Currently the Magento instance I mentioned is still running on version 2.3.3, as soon as I have updated to 2.3.4 I will report if both extensions behave as desired.