I had upgraded the PHP version from 7.1 to 7.2 and also the Magento2 version from 2.2 to 2.3x community version, since then the Vendor panel is not loading and is just showing a blank page. If I disable the separate dashboard, the panel loads in the customer account.
You can disable Magento_Paypal and Magento_Braintree, the page will display normally.
Hope this can help you! Let me know if you need further assistance.
If issue solved, Click Kudos & Accept as Solution.
Both the Payment gateways are already deprecated and disabled, yet we are facing the same issue.