Glad to have you here, @nk--quick!
Allow me to share a few information and help you correct your expense transactions with double entries.
To start, creating an expense transaction or writing a check using your Paypal or AMEX bank account will create a double entry in your register. This is because you've connected both your Paypal and AMEX bank account to QuickBooks Online banking.
For example, creating an expense transaction using Paypal bank account and your AMEX bank account as the expense account. This as one of the possible reason why it creates a double expense entry.
I've attached a couple of screenshots below for your visual reference.
With this, you'll have to select only one bank account when you create an expense transaction. Thus, making sure to select an expense account under the Category details to avoid double expense entries.
Feel free to leave a comment below if you have any other questions with expense transactions. I'll be always around to help.